Here's an example. I purchased a Fab Blue Hammer and a Fab Burgundy Hammer back in 1995. Bill Hall, who designed the Blue Hammer, shared with me recently that the Blue Hammer's and Burgundy Hammer's differential were both about a .020; their RGs were 2.51 and 2.52, respectively.

I'm guessing that a high differential back then was anything in the .030s, probably as high as the mid-.030s. I'm curious if anyone might recall what was considered a high differential ball during that era?

1990/91 Brunswick Phantom was RG 2.458 Diff .046 and Int dif .020

1995 when the Brunswick Zone was released they were RG 2.50ish and Dif of .047.
1993-1997 Brunswick Rhinos were RG 2.55 and Difs of .023

Quantums of 1994 were RG of 2.55ish plus and diffs .023 to .032
Quantums in 1995 were RG of 2.51ish and difs of .055

Columbia Cuda/C of 1995 Rg 2.50 Dif .058
Columbia Boss of 1997 Rg 2.51 Diff .051

Track 1995 NRg was listed as low RG and high Diff but cant find the specs
Track Synergy of 1996 Rg 2.607 Dif .050
Track Triton Blue of 1997 Rg 2.46 Dif .042
Track Synergy ETS of 1997 Rg 2.63 Dif .070

For the most part across the board in 1995 is when most manufactures started going with the more dynamic/aggressive cores. I started bowling in YABA 1996-1997. Since I was just getting into bowling I remember seeing all of this first hand and how things were advertised ect. The Zone was the it ball of that time locally followed by the Columbia Boss line then Later the Ebonite Wolf series. The Ebonite Omega line was the first main run of seeing asymmetric cores in a line.

There are many bowling balls today that use lower diff cores and still have plenty of hook to offer. First hand for me the Brunswick Slingshot diff .017 Strike King diff .028, The Ringer series Diff .038. All of these ball will work well on todays conditions. In many cases they can cover plenty of boards.

As I've posted elsewhere, I was away from bowling for 18 years (1996 until January 2014) and I've had a lot to catch up on. If I've listened and read correctly, the cores and coverstocks from the mid-1990s are not as strong as these newer ones, especially those that were designed for heavy oil. Taking the Track NRg, for example, it would appear that ball would probably compare more favorably to the Brunswick Ringer series in terms of RG/differential; it would be a ball better used for short to medium length oil patterns with medium to dry oil volume.

Would that be an accurate guess?

The difference between then and now isn't as big as you think. The Track NRg core specs aren't posted online but are likely close to other balls being RG 2.5 and dif. .040 to .050.

These cores are larger flaring cores which can lead to more hook. The change in coverstocks over those next few years was the other part of the equation.

It has been posted that there is very little change in bowling ball technology since the early 2000's. That is hard to promote if you are in the business of selling new bowling balls obviously.

If I recall the Navy Blue Phantom was the ball that was the ball that topped low rg and diff..  No other ball could be lower in rg or higher in diff (at that time).. 2.43 and .080 ..

Obviously the diff rule is now .060

Flare is only relevant if the ball slows down properly after that the strength of the core effects how the bowling ball transitions - bigger core bigger transition

The more important number is the core diff that dictates much more than RG value

There was a few camps that thought this was the new direction in ball motion...when I was with Brunswick I believe it was the Twisted Fury that had a intermediate diff of .025 or so and the primary was .035 or so...to me this creates confusion in the core what controls what...and honestly ball motion isn't and shouldn't be that difficult
That's why for the guys I work with (you included) I like the lower diffs easier to control and create better ball motions