An 'outside the box' one for consideration, given date and location:
CROSSAN
MARY
PETER CROSSAN/ROSE CASSIDY
F
23/7/1846
4/8/1846
Airdrie, St Margaret's
Could something have happened to this couple and Mary have been brought up by James' family as their own and never having known different 'parents', used James and Rose's details on her marriage, and likewise whoever registered her death used them?
Haven't time to track through census etc at moment to check.
The mother of the 1846 birth, had maiden name Cassidy and an earlier post on this thread lists a "Cashaday" lodging with James Crossan and family in 1861. Might just be coincidence though.
As the 1842 Lennoxtown birth of a Mary had the correct MMN, ie Bradley, based on the 1927 death of your Mary, where have you found a record of that Mary's death to be so sure she isn't the, regardless of age variations, same Mary who married Neil(l) Toy(e)?
CROSSAN
MARY
76
BRADLEY
1927
486/ 8
Muiravonside
TOYE
MARY
76
BRADLEY
1927
486/ 8
Muiravonside
Your Mary's death in 1927, would suggest an 1851 birth, so again a variation, but not uncommon.