Hi Jean,
Very curious, !
Before i saw your comments about entries which do not exist, I actually emailed the Manchester Register office with the reference number and details, saying it showed up in Ancestry and yet not the other online indexes, but asking them to check on the reference.

Looking at the batch when you click on the reference page number 8c 769, there seems to be 9 entries, 5 from Bolton, Greater Manchester which have images, and 4 from Chorlton, Manchester. These 4 have no images, yet all 9 seem to have the 769 page references. I tried looking up the other Chorlton entries in FindMy Past, one for CANDLIN comes up in 1915 but different quarter and district!; two other Chorlton ones dont show up at all in FMP for 1915.

So presumably it looks like Ancestry has somehow messed up something in their FreeBMD index.
When i have heard from Manchester i will try and contact Ancestry, unless anyone can find an answer!
Richard