My understanding of the waiver is that the ticket is worth the same as money : you can bring it to another carrier and apply that value to another ticket.


That's what the Star Alliance Reference Manual states, in regards to SQ, so it seems correct that they required the endorsment:



Endorsement Waiver
Each carrier will publish and honour the Star Alliance Endorsement Waiver Agreement (EWA) policy 1, as agreed on a
bilateral basis between Star Alliance member carriers.

Any Star Alliance member carrier or one of its agents will be able to reissue or exchange a ticket or MCO without having to
request a written or stamped endorsement, under the following conditions:
1 Exceptions apply to SQ.

Voluntary
• When a customer requests a change of airline or re-routing (as described in IATA Resolution 736), the two Star Alliance
member carriers agree to waive the endorsement requirement between themselves for non-restricted tickets or MCOs
provided that:
A. such tickets or MCOs do not bear carrier validation restrictions, which by their terms prohibit the transfer of the ticket
or MCOs such as “Valid on XX only” and “Non-Endorsable”
B. such tickets or MCOs are not governed by fare rules which prohibit transfer of the ticket to the other party
• No endorsement required for First Class, Business Class, full Economy Class and non-restricted excursion fare tickets
• Does not apply to ID /AD tickets.