I'm a statistic geek and compiled USAAF confirmed victory credit data downloaded from the Air Force Historical Research Agency a few years ago. Your post prompted me to do a refresh on the data I got from AFHRA and run the analysis again when I found my numbers didn't closely correspond to any totals in the thread thus far.
The USAF Historic Research Agency admits that a few of the type of reports used to assemble this victory credit data are missing so actual counts may be higher. I'm not sure if any missing reports involved 354th FG data or not.
The victory tallies shown below for the 354th FG are confirmed destroyed in air to air combat, not strafing kills, nor probables or damaged claims. To quote AFHRA: "The enemy aircraft had to be airborne, heavier than air, manned, and armed. Destruction involved shooting an enemy aircraft down, causing the pilot to bail out, intentionally ramming the airplane to make it crash, or maneuvering it into the ground or water. If the enemy airplane landed, despite its degree of damage, it was not counted as destroyed."
Using their data, my analysis shows the following:
353rd...289.5
355th...139.66
356th...160.08
354th (group level echelon)...15
Group total: 604.24
This total represents the victory credits awarded to pilots in the above named "echelons' at the time the claim was filed as they appear in the AFHRA data, for all years 12.7.41 - 9.2.45, & all theaters of operation.
I can't comment regarding why such a discrepancy exists. There are myriad potential reasons and possibilities. Exact and unquestionably accurate victory totals may be hard to come by, but no doubt the 354th made quite a contribution in WW2.
Hack9
AFHRA Link:
http://afhra.maxwell.af.mil/index.asp
