Eng and Maths Initial Assessment Dates

There isn't really a hard and fast rule.. but best practice would suggest they're conducted as close to the start date as is reasonably possible, to reflect their most current level. If you think you could cogently defend using results from the same calendar year where the initial assessment was conducted say, 10 months prior, then that's entirely your prerogative. I'd personally be slightly skeptical, and would prefer the 3-6 month approach of the 2 you've mentioned, but consistency is the main thing.