According to PFF Hawk has a total of 560 solo tackles and 134 assists in the regular season since 2007 (PFF doesn´t have any stats for earlier seasons). According to the NFL´s unofficial official stats he has 545 solo tackles and 257 assists over the same time period. It seems like the Packers are way off in their assessment.
Then there's the 3rd. set of numbers.
The unofficial official stats from nfl.com, presumably from the official game scorer, total 921 solo+assist for his regular season career. The Packer press release gives him credit for 1,118 tackles. The press release does not indicate if they're throwing in playoff numbers. Even so, 12 playoff games would not account for 197 tackles.
Your comparison goes to illustrate that a solo tackle is relatively easy to identify whereas "assist" is a very squishy concept. I'd put "assist" on par with "pressure"; some imagination has to be applied as regards the outcome of the play in its absence. For example, if an ILB anticipates to the right hole, redirecting the runner into another player's tackle, does one scorer give him an assist even though he never laid a hand on the runner whereas another scorer does not?
How about Hawk's many late appearances at the ball these last few years? Are the Packers scorers more generous in this regard?
Clearly PFF more stringently constrains the imagination as regards tackles...or at least the guy(s) grading Packer games are more discriminating. I would not necessarily be confident of consistency from one PFF grader to another...just as the unofficial official scorers might count differently. Further, I'd be a bit skeptical of PFF's numbers prior to 2013. If memory serves, they did not have all-22 coaches tape until nfl.com started supplying them in 2013, though they're likely better than the official scorer's on-the-fly assessments.
The minor discrepancy in solos does beg a few questions. If a guy is run out bounds, is that a tackle for one scorer and not for another? Before Hawk cut his hair, was there an occasional confusion as regards the identity of the tackler?
My takeaways:
1. Solo tackle counts probably have some merit.
2. Beware the assists.
3. It's safe to assume Ray Nitschke is the all-time Packer tackle leader even if they were not being counted.