I'm sure that others may have noticed, but there are major indexing problems for the 1911 Census. About one third of the residents of Anglesey are shown as having their Place of Residence in another county- Caernarvonshire(sic).
This might totally mislead researchers from around the world.
This appears to be a data error supplied by the national Archive, as the fault also appears in Find My Past.
The error stems from the fact that the Registration Districts covering South and East Anglesey in 1911, were Bangor and Caernarvon(sic) which are both in Caernarvonshire(sic). It would appear that the National Archive therefore deemed that those parishes in South and Eastern Anglesey covered by these offices, were therefore in Caernarvonshire(sic).
For the record, these parishes really are in Anglesey, but Ancestry says they're in Caernarvonshire:
Llanfair yn y Cwmwd,
Llanfihangel Tyn Sylwy,
Penmon,(& Puffin Island),
So, if you've spent some time trying to find people in these parishes in Anglesey- they're not there, they're misfiled under Caernarvonshire(sic).
To further add to the fun of searching for Anglesey ancestors in 1911, you must remember that probably 80% of the forms were completed in Welsh. Most Welsh speakers if born on Anglesey, would have put their Place of Birth as "Sir Fôn" (County of Anglesey), or "Môn" (Anglesey).
This has totally thrown the transcribers who have misinterpreted "Môn" (Anglesey) as "Mon." (A one time abbreviation for Monmouthshire some 180 miles away).
Thus, if you look at the transcriptions, you will see that a large proportion of Anglesey residents in 1911 were supposedly born in Monmouthshire.
I was raised in a small hamlet in Anglesey,and in 1911, it had 136 residents living in 33 dwellings.
These people of course are not only erroneously indexed as living in Caernarvonshire(sic), but bizzarely 79 are indexed as having been born in Monmouthshire.
I have notified Ancestry.co.uk of these errors, but am not holding my breath for a speedy correction.