Good spot, technically bang on, it's simply income not a 'pension' until then. Let's think about this. It's a given that if you rejoin and have a 'pension' (official terminology) in payment, it gets suspended or reduced to ensure that it, and your new FTRS pay does not exceed your old rate of pay (adjusted for inflation). But, if you join FTRS, and especially if there is a gap in employment, and if you have transfered your AFPS preserved pension benefits (as you say, still 'EDP') into a personal pension, what then?
You might not even take income from it, your personal pension might remain completely untapped or uncrystallised (lots of new tax benefits too!). If your income therefore, is lower, how would that affect your FTRS rate of pay? Your new personal pension would be an asset in much the same way an investment portfolio accrued via your salary over the years is an asset. In respect of surrendering EDP lump sum, what about reverse commutation (especially if above was achievable)?
It'd be interesting to see if the scheme rules could be lawfully interpreted to one's financial advantage and whether or not anyone has done it.