Back in the pre e-ticket days, a physical ticket was a booklet with 4 vouchers. Each booklet had it's own ticket number.
Your 20 segment xONEx would be comprised of 5 such books of vouchers, often presented stapled together. The five 'tickets' would be recorded in the GDS's under the one PNR.
So 'Many (tickets) to one (PNR)'. I didn't think it could be done the other way.