Moving LB2 a month ahead because of the Anniversary isn’t too unusual. NA already did something similiar during the first Anniversary with regards to Camelot.
In JP of 2016, Camelot was released on July 25 and the first Anniversary was released on July 30. Since the Anniversary was released after Camelot, it meant that Lancer Artoria could be added to the GSSR.
If NA decided to keep the original release date of Camelot it would mean that Camelot would have been after the Anniversary so Lancer Artoria wouldn’t have been on the GSSR. The NA version had already received a bunch of criticism and complaints because of how the 2017 Thanksgiving GSSR was too early and Mordred and Jack didn’t end up on the lineup unlike the original GSSR. So since the NA’s first anniversary was a month early, Camelot had to be released a month early in order to fit in Lancer Artoria which is why we got it June 28 instead of July 25.
So since 3rd Anniversary is expected to be released a month sooner, it’s also expected that LB2 be released a month sooner in order to ensure that Napoleon is added to the GSSR and so people have access to LB2 materials that are needed by Skadi.