My understanding is that those clauses only come into play with pilots who are deemed to be in surplus once the chairs are all filled.
For example, what if EVERY 300 Captain in BNE bids for the 400? There's no spot unless some come up as a consequence of other movements or the company exercise some EOI slots. So does the company give a 400 spot to every Capt on the 300 that bid who has seniority to hold one, making X amount of BNE 400 Capt's now surplus?
Or does the company fill what positions it can on the vacancy notice. Those capt's who don't get their bid and are surplus to requirements on the 300 get to bid for 400 FO slots if they desire?
No one has come out and said how the whole process will work.