Have just seen all this. The fully history of the CAT exploration of Croesor, to date (I do have some further ideas), is written up in "The Mine Explorer" Volume V although on looking at part of it tonight I realise that I have got one date wrong since the 3rd paragraph on page 45 should refer to 1981 rather than 1989.
It would appear that CAT were the first to do this trip and this ties in with the facts since the through trip as we know it today would have been impossible without the water level having risen and CAT were exploring as the water came up.
A similar exercise was undertaken by CAT members when the pumps were switched off in Maenofferen.