I have been giving these Armstrongs some thought.
We have:
1. John Armstrong and Sarah, b about 1670-1680 They have one documented son who survived to adulthood, William b 1701 in Riseley.
2. William had two sons that we are aware of - John born in Riseley in 1729 and Thomas born after the move to Wilstead in 1734.
3. Thomas married Christian and he and his descendants populated Wilstead and Haynes and parts further east with Armstrongs.
4. John married Edith and produced two sons that are documented: William b 1754 in Wilstead who went off to Cople via Maulden, and (according to Bob's tree) populated Cople, Goldingdon and Blunham - and John b about 1760 in Wilstead who appears to have ended up in Ravensden, probably also via Maulden, as that's where his parents died. One of John's daughters was Edith.
Now, at the same time, we have:
1. Samuel, b about 1760-1770 who married Sarah and produced first (and only?) daughter Edith in Elstow.
2. Thomas, b about 1760-1770 who married Phoebe and produced first daughter Edith in Upper Gravenhurst .
3. Jos (Joseph/Josiah/Joshua?) who turned up in Thurleigh in 1788 and married another Sarah, Sarah Beal. They haven't any documented children that I have found.
None of these three are recorded on the IGI until their marriages, and Thomas's marriage is a member entry not an extraction. Tho' the baptisms of his children do confirm the marriage to a Phoebe of one ilk or other.
Now - is there a possibility that Thomas and Samuel at least were unbaptised sons of John and Edith, born either in Wilstead or Maulden?
It seems likely that John and Edith were pretty poor, or the Maulden overseers would not have paid William's apprenticeship bond in 1766, well before either of them died.
And although Beds is pretty well doucmented on the IGI, there are no baptisms in Beds which fit any of (1) to (3) above that I have found.