I had been doing it almost as long I've been reloading--Checking one manual against another. Our own member, the esteemed, the venerable, the laconic,
C.R.Sam, taught me the use of the verb phrase,
"to second source," for this practice. As in, "You should second source that data, sonny boy."
There is always a possibility, however slight, of a misprint or an out and out error in a given manual. Or, a particular compiler may well be honestly reporting HIS data, but his instrumentation might have been off on a particular day.
I can recite, from memory, good, safe, load information for dozens of cartridges or variations thereof. But except for a very few old stand-by formulae, I won't put 'em out for others without checking my notes, or at least a manual or two, to verify that they are within normal limits. And, you know what? I do not resent in the slightest when someone takes my load tips and cross references them in his/her books. I applaud such care and caution.
Like
Jeeper, I rgularly take advantage of the manufacturers' hand out pamphlets. Every handloader should look at the freeby rack in the gun shops, to see if Alliant or IMR or whomever have sent out new booklets. I like to keep back issues, too, just in case a particular powder or bullet is discontinued and I happen to have a stock on hand.
Best,
Johnny Guest