A somewhat relevant thought.
I replaced my old iron set Tommy Armour 845s this year with Titleist 718 AP1 iron set. I compared lofts on the irons. I found that the 845s irons had 4 degrees of separation on almost all clubs, the AP1 irons had 3, 4 and 5 degrees of separation, increasing with higher number clubs. Also, the 845s 3-iron has the same loft as the AP1 4-iron, and the 845s 9-iron is different by 1 degree from the AP1 pitching wedge.
I had to carry a note card in my bag to remind me of the differences (image attached).
There might be specific reasons for loft differences between AP1, AP2 and AP3 irons. I think the pros will adjust lofts to suit their game.
I also think that there is no standard among club manufacturers for club lofts.

Hi Jerry, We separated our iron sets into two teams. The distance category vs Tour category. The distance category has the AP1, AP3 and T-MB irons and the Tour category has the AP2, CB and MB irons.
The AP1 is for the player that wants maximum forgiveness and maximum distance in a great looking head. The AP3 was created for the player that loved the look of the AP2, but wanted more distance as well as more forgiveness. The T-MB is called our technical muscle back - we originally just created the long irons, which were so well received that we designed the entire set. It looks like a muscle back, is approximately the same size and shape as an AP2, but launches higher with less spin. Although many of our Tour players have it in their bags as long iron replacements, this club has the combination of forgiveness and distance.
The AP2, CB and MB are the Tour irons and as such have more traditional lofts. The AP2 irons are one of the most played on Tour and have been at the top of the iron category since we introduced them in 2007. The players on Tour did not want (or need) the stronger lofts - what they wanted was playability and precise distance control.
Long answer, but that's why you see the loft differences between the AP2 and the AP3.

Cathi, Thanks so much for the explanation on this. It's completely understandable the tour players want playability and more important distance control. You go to a tour event and sit on a par 3 and you find a lot of them may miss it a little left or a little right but a lot of them are at least pin high. At least that's what I have noticed before.

Jerry S. I have heard this statement many times and it astounds me. I have a teacher who sells many different manufacturers of clubs and he told me this years ago.

"I also think that there is no standard among club manufacturers for club lofts."

There are no standards in golf in lie angle, lofts and shaft length and flex. In 1970 the seven irons generally had a 40 degree loft while by 1990 loft had strengthen to 36 degrees while the length had increased from around 36 inches to 37 inches, but, again no absolute standard. Today players clubs are generally between 33 - 35 degrees in loft with distance and game improvement clubs coming in anywhere between 30 - 32 degrees