I was going to make a long story out of this, but decided to just give a direct answer: legal SKF with a qualifying 2X2.
There is no minimum number of exceptions required nor maximum number of exceptions allowed. But, to have ANY exceptions, they must have a compliant 2X2, which means all 5 positions filled. If they have a compliant 2X2 in a SKF, then all 5 of those linemen in the 2X2 are ineligible by position, and any of those linemen wearing a number other than 50-79 are ‘exceptions’ to mandatory numbering. (Effectively, they all become the otherwise required 5 linemen numbered 50-79.) Once they are in position in the 2X2, and the snapper is in position, they are “locked in” to their positions in the 2X2. They may not move to any other position(s), either within or outside of the 2X2. A vacant position(s) in the 2X2 may be filled, but, once a 2X2 position is filled and the snapper is in position, that lineman/linemen is/are locked in.
The linemen outside of the 2X2 are governed by other alignment and eligibility rules. Those linemen are NOT locked in to their positions, and may move to other positions on the line or in the backfield. If on the end wearing an eligible number at the snap, they are eligible. If interior, regardless of number, they are ineligible.
Violations of these rules are all LIVE-BALL illegal formation fouls.
That’s the short and long of it.
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Gotta add something important I failed to mention. If Team A actually has 5 linemen numbered 50-79, then they are not restricted in formation, changing positions, and making substitutions, beyond any other scrimmage down.
