I do not actively research, but draw upon accumulated knowledge, my files plus resources gathered over seventy years.
To assume, guess or speculate is wrong!
Yes! many get mixed up or tell porkies.
All possible known James Corletts’ have been looked at by me and discounted.
I have also discounted the other James Radcliffes you have mentioned.
As over three hundred years on the Isle of Man the surname “Corlett” etc. was the second most used and it will appear on nearly all half decent Manx family trees.
Any true blood “Corlett” is related, my children are half manx Corletts!
Intermarriage is a key word and as we are all loosely related do not over rely on dna.
Rather than carrying on with this scattergun approach I advise you start again with yourself following the full paper trail in the North American sub-continent including not only with what he claimed on his marriage registration but revisit all ports of possible entry.