I would be using nothing but the older manuals if it wasn't for worrying about changes in the powder itself. Meaning its possible that powder X might have a different composition and burn rate today than it did 30 years ago. I have no proof of this, but it's something I consider.
We have thought of this also, and did some testing on some of it. But first a word about the Hodgdon surplus powders.
After WW2 Bruce Hodgdon made a deal with the US, to buy all their surplus military powder. He had great amounts of the powder that would later be named 4831. (all his powders have the letter H in front of their designation letters.)
He was in such a rush to get all this really low priced powder into the hands of the hordes of shooters who appeared like magic after the war, that he put this one slow burning powder out there, before he had fully tested it. He knew it was slower than 4350, thus it would be safe to use it in place of 4350. So he put this slow powder on the market, calling it "4350 data powder." In other words use it like you would 4350.
Before too long Jack O'Connor, in his monthly column as shooting editor of Outdoor Life Magazine, came out stating he had developed a great load for the 270 Winchester. He said put 60 grains of this new Hodgdon powder called 4350 data powder in a 270 Win case, which will fill it right to the top rim of the neck, sometimes requiring some tapping of the case, to prevent it from over flowing, and force a 130 grain bullet into the case.
Soon masses of handloaders were singing the praises of this 270 load, using the new surplus Hodgdon powder.
When I started handloading I have stated it was Norma components I started with, but one of my first purchases of other powder, was a 50 pound keg of the surplus Hodgdon powder, by then named H4831.
In a Bruce Hodgdon memoir, he states that when they did their scientific testing on their surplus powders and published the ratings and loads for them, they never even bothered checking the famous Jack O'Connor 270 load! He said many thousands of happy handloaders couldn't be wrong, so they simply entered, 60 grains of H4831 in a 270, with a 130 grain bullet, into their loading charts!
I think it was in the 1980s that Hodgdon's were running low on 4831 surplus powder, so they newly manufactured it (or had some other firm make it for them.) They stated to just use the same loading data for the new powder, as they showed for the old surplus powder.
On Aug. 20, 1991, I got around to testing if there was any difference between the two powders. I took ten 270 cases and used the same standard large rifle primers in all ten. With five I loaded 60 grains of the old surplus powder and the other five I put in 60 grains of the new manufactured H4831, topped each case with a 130 grain Herters bullet, and shot them in my 270 Sako.
Here are the readings from the Oehler 33 chronograph.
War surplus H4831 powder, average speed 3078, with es of 33.
Newly manufactured H4831 powder, average speed 2960, with a es of 45.
As stated previously, I used my Ruger 77 in 243 with 47 grains of either Norma 205 or the old H4831 powder with a 100 grain bullet.
Last year I got a new Marlin XS7 in 243. To start a load for it, I looked at Hodgdon's loading chart. Not the one on line, which shows a 243 with 100 grain bullet as a max load of 42 grains of H4831, for a velocity of 2924, but the Hodgdon loading chart in the 1964/65 Ellwood Epps catalogue. It shows 243 Win, 100 grain bullet with 46 grains of the old war surplus H4831, for a velocity of 3009 fps.
I had no qualms about loading this load into my new Marlin, because the load was a full grain under my standrd load in the Ruger 243, of 47 grains. Plus, I had already shot other loads with lighter bullets and found nothing wrong with the new Marlin.
I still have some original war surplus H4831 which I purchased in the mid 1960s. I loaded 46 grains of this old powder into 243 cases, topped with a 100 grain Sierra bullet and shot them over a "chrony."
No sign, whatsoever, of excess pressure and the Chrony showed a velocity of 3073.
If I test the same load, only with new Hodgdon's H4831, I will let you know the results.
Best wishes, Bruce