I assumed his refernce to "recievers and covered" being eligible by number but being covered up on the outside, not an interior lineman.
Correct me if I am wrong, but, if he is "covered," then he is on the line, but has at least one fellow lineman (by definition) outside of him, even if he is spread wide, and the covering player(s) is/are spread wider than him. This has nothing to do with numbers - strictly position. On the line and between the ends = ineligible. On the end of the line with a number 50-79 = ineligible. On the end of the line and wearing a number other than 50-79 = eligible.
I realize that the bigger question may be: Are these guys on the line or in the backfield? Yeah, that is a mess, these days. Who are on the line? Who are in the backfield? Who are supposed to be in the backfield, but are up in the line, wearing an eligible number, but covered by an end?
This is an issue that necessitates preventive officiating in the first few minutes of the game. With each team's first possession, work to get the linemen on the line, and the backs in the backfield. After a warning to an ambiguous player and his head coach (not just a position coach), flag 'em.