Jonathan Mason in the 1810 census of Frederick VA seems surely significant and must be accounted for.

1810 census VA Frederick p.350/558:
Jonathan Mason 1 male over 45, 1 female over 45, 1 female 10-16

By purely speculative description, a case can be made that this Jonathan is of a previous generation. He is certainly located close to the 3 brothers and his neighbors' names in the census support that he is in the same neighborhood as the brothers.

The wives of Reason, Bingley, and Andrew are all in the 26-45 category in 1810; they are actually in their late 30s to very early 40s. Jonathan's wife is already over 45. If this Jonathan were another brother we might expect more children. The 1 female age 10-16 could be a last daughter at home; she would be so much younger than Reason, Bingley and Andrew that she would almost have to be by a second wife. If she's a last daughter born in the 1790s, previous children could have been born as early as the 1760s, i.e. parallel to Reason, Bingley, and Andrew.

The tax lists still need to be fully extracted and collated, but in the 1800 Personal Property tax lists in the M lists Jonathan is listed near Andrew and "Rezon"; Bingley is two pages away; all 4 show 1 white, 1 horse etc., tax amount of .12. That Jonathan is still taxed means he hasn't reached the age of exemption (I'm not sure if for these years it's age 50 or 60). There don't seem to be land or probate records for this (older?) Jonathan in Frederick VA and he does not appear in the 1820 census in any state.
****Is Jonathan the 2nd male over 45 in the household of Andrew Mason in the 1820 census in Frederick VA?

The children of Reason, Bingly, and Andrew who live to 1880 report a mix of birth places for their parents, both VA and MD. This inconsistency is not unusual and both places must be explored. That Bingley married Babby Free in MD further supports the need to explore MD. The following set of records is a start at linking the Frederick VA Jonathan to the Jonathan of nearby counties in MD.

Revolutionary Patriots of Montgomery County Maryland 1776-1783 by Henry C. Peden Jr. 2001
[This source also has the information listed in the next book, but collated by name; I have used here only the information not included in the next book.]
Jonathan Mason - 1777, lived in the Lower Part of Newfoundland Hundred (2 taxables).
Jonathan Mason, Private, 1st Co., Lower Bn., Militia, Sep 1777.
Archibald Mason, Private, 1st Co., Lower Bn., Militia, Sep 1777.

Revolutionary Records of Maryland by Gaius Marcus Brumbaugh and Margaret Roberts Hodges
p.3-4 Montgomery County, Maryland, 1778 These appear in Peden's book as oaths of allegiance taken 28 Feb 1778.
The Worshipfull Edward Burgess' Returns
#191 Jonathan Mason
#281 Richard Mason
#343 Alexander Mason

p.24 Frederick - Patriots' Oaths of Fidelity and Support, 1778
Oath of Fidelity and Support Taken Before Justice John Lawrence, 5 March, 1778, 98 Citizens
#38 Mason, Jonathan
[Note: the oaths were taken by men of 18 years and above]

The Maryland Militia in the Revolutionary War by S. Eugene Clements, F. Edward Wright 1987
Appendix B - Muster Rolls and Other Lists Montgomery County
p.198 Montgomery County, Lower Battalion
1 Co: ...Archd. Moson [sic]...Jo: Estep...Basil Burton...Capril Holland, Jonathan Mason.... (Militia Lists of Daus. of Founders and Patriots, held by Md. Hist. Soc.)
p.205-207 "The List of the different companies in the lower Battn. of Montgomery County, with the different Classes as returned by Coll. John Murdock 15 Jul 1780 - "
2nd Company: [Officers] 2nd Sergt [Sergt by ditto] Joseph Estep...3rd Corpl [Corpl by ditto] Archd. Mason...
Class No. 4 [all names]: Joseph(?) Browning, Robert(?) Orme, Alexander Mason, ..ngley Mason, Joshua Lazier, Solomon Miers, Joshua Lazinby, John Jones, Wm Newcomb.
Class No. 7 [all names]: Jacob Burton, Thos. Mitchell, Jereh. Browning, Capil [sic] Holland, Jonathan Mason, Joshua Swain, Thos. Dawson.

Comment: The "..ngley Mason" sure looks like a pretty good smoking gun. The Reason, Bingley, and Andrew of Frederick VA were born 1766-1770; these namesakes serving in Maryland in 1778-1780 have to be some number of years older, possibly an older generation. One mystery is why we don't see "..ngley" Mason on any oaths of allegiance.

http://query.mdarchives.state.md.us/
MD Montgomery Assessment of 1783
Jonathan Mason. MO Lower Newfoundland, Rock Creek, and North West Hundred, p. 7. MSA S 1161-8-2 1/4/5/51
Richard Mason. MO Lower Newfoundland, Rock Creek, and North West Hundred, p. 7. MSA S 1161-8-2 1/4/5/51
Alexander Mason. MO Lower Newfoundland, Rock Creek, and North West Hundred, p. 11. MSA S 1161-8-2 1/4/5/51
Archabald Mason. MO Lower Newfoundland, Rock Creek, and North West Hundred, p. 11. MSA S 1161-8-2 1/4/5/51
Patrick Mason. MO Lower Newfoundland, Rock Creek, and North West Hundred, p. 11. MSA S 1161-8-2 1/4/5/51
Richard Mason. Rogers Chance, 100 acres. MO Lower Newfoundland, Rock Creek, and North West Hundred, p. 20. MSA S 1161-8-2 1/4/5/51

Frederick MD Lutheran Marriages and Burials 1743-1811 by Frederick Sheely Weiser 1972
p.44 - 10 Aug 1785 Jonathan Mason md. Salah [sic] Parkison, both widowed, proclaimed 3 times. witnesses: Frederic [sic] Haux, Peter Beltz.
p.53 - 31 Jul 1787 Johannes Schindler md. Eleonara Lahe, proclaimed. witnesses: Jonathan Mason and his wife Sarah.

1790 MD Census
I have included the Free families that are in these counties, there are other Frees in other counties of MD.
Frederick Co:
p.227 Robert Mason 1-0-1
p.250 Jonathan Mason 1-0-2
Montgomery Co:
p.14 John Frees 1-0-0
p.60 Alexander Free 1-1-4
p.243 Nicholas Free 2-2-2
p.249 Archibald Mason 1-0-0, 2 slvs
p.257 Alexr Mason 2-0-5, 4-0-1 [free yellow and blacks >16, <16, females]
Washington Co:
p.20 William Mason 1-1-2

Baltimore Co Marriage Licenses 1777-1798 by Dawn Beitler Smith 1989
19 Oct 1792 Bingley Mason and Babby Free [license]
22 Oct 1792 Bingley Mason md. Babby Free [minister's return]This is the next generation Bingley, b. 1767-1770, brother to Reason and Andrew. His land records in Frederick VA show Babby as Barbara.

Researcher Francis Mason has studied the Frederick VA tax lists and says the Masons show up there in the late 1790s. The 1800 MD census below shows that Jonathan Mason is no longer there.
1800 MD Census
There is no Jon* Mason, no Robert Mason in MD.
Frederick: no Mason
Montgomery:
Distr 3: Daniel Mason
Distr 4: Archebal Mason, Archeball Mason
Washington: no Mason