The impression I get is that if an age has been recorded in months or weeks (not sure about days) that number will show in the GRO age column, and appear to represent years, which should show 0 or perhaps 1.
My experience is that is sometimes the case but not always sometimes the deaths do say 0 identically to FreeBMD. Post 1900 most seem to say 0 rather than have a numerical value (which should be months).
As you say as long as one is cross referencing to FreeBMD, Ancestry, Findmypast etc old indexes and verify it is the same person using the Vol & page nos it is additional useful info.
Has anyone investigated the difference between "phonetically similar" and "similar sounding"?
There was a reply about that earlier this week possibly in the lengthy locked thread but there are several similar on the go. The reply was basically google the terms but you get rather technical/mathematical info about replacing letters. Basically the Similar sounding is looser than Phonetic just as Ancestry's order is Exact/Sounds Like/Similar/Soundex.
I try to avoid using anything other than Exact on the GRO, find it takes ages & often times out.