Help Figuring out the connection

[Nora]

Hello! I need your help again haha. Ok, I so got my great aunties (Annie Heffernan) wedding cert today and one of the witnesses is a Margaret Robbins and I knew there was a connection to her because I found a birth for a child Thomas Robbins born 1924 with MMN Heffernan so assumed that Margaret Robbins was Margaret (Maggie) Heffernan born 1894. She was on the 1901/1911 census with Annie as her sister. I got Margarets birth cert that someone on here found for me when I 1st posted. Her birth name is Margaret Fox. No father on birth cert and the mothers name match up but it says she's from Ebbw Vale instead of Abergavenny where all the other records are listed and it also says she in the workhouse in Tredegar. I found a marriage record for Margaret Fox to a Thomas Robbins in July 1919 which makes sense cos she's Margaret Robbins on Annies wedding cert in Dec 1919. My problem is that on the 1939 register her birth is 1874 with 94 above the 74 but I don't know if it's a date correction or if it's part of some number code thing that's sometimes above names, if that makes sense. Also her husband Thomas was 15yrs older than her, how common was it for someone to marry someone that much older than them in 1919? Also think I found her death record and her birth is 1888 on that. There's also another Margaret Fox born in 1888 with MMN and location matching up but on the birth cert fathers name is William Fox not Patrick Fox which who I think would've been the father but the father to all the other children is William Heffernan and because MMN changes between Pulling and Fox it just makes my head hurt. I hope this makes sense and you can help me work out which Margaret turned out to be the Margaret Robbins that was a witness at Annies wedding.

[pinefamily]

My maternal grandparents married in 1922, with a 13 year age difference between them.

[Nora]

Yeh I suppose the age difference isn't a big deal. It's more the not knowing if it's the right person or not or if the other Margaret born in 1888 is also a relative. Maybe the one born in 1888 is the one on the census's but the dates are wrong. I dunno. It would all fit if there wasn't 2 Margaret Fox's that could both be the right one.