For my own benefit a few days ago I was looking at the information for all the North Wales summits and plotting them on the Radio Mobile Mapping Program. I found 8 summits where the Locator information given on the summit information pages does not agree with that calculated (by the program) from the given Lat/Long information. Whilst all of those summits are close to the edge of one or more squares I would have expected the two bits of information to match.
The summits that this applies to are NW-011, NW-014, NW-016, NW-019, NW-024, NW-027, NW-046 and NW-073.
I have tried putting the NGR’s from the SOTA pages into the page at http://www.carabus.co.uk/jscalculators.html .
This also gives the same difference in Locator information (except for NW-011 where the difference is as little as 10m in the NGR value).