Understanding GIB Bid Descriptions said:
Suit Quality
3-card: exactly 3 cards
4-card: exactly 4 cards
biddable: 5+ cards, or 4 cards + 3 of 5 honors or more than 4 8421 points
rebiddable: biddable + 1 card
twice rebiddable: rebiddable + 1 card
3-card: exactly 3 cards
4-card: exactly 4 cards
biddable: 5+ cards, or 4 cards + 3 of 5 honors or more than 4 8421 points
rebiddable: biddable + 1 card
twice rebiddable: rebiddable + 1 card
So, North's spade suit is "biddable", not even "rebiddable", never mind "twice rebiddable" as stated in the description of the 4♠ bid. There's no reason this bid should show anything more than simply 5+ spades. Why embellish?
Also, should the 4♠ bid have an upper limit? Is it an offer of a final contract if South is at a minimum for his reverse?