no. a reservation code does not mean you are good to go.
all it means is that the airline has a reservation for you.
unless the reservation is paid for it will be cancelled. That can happen right up till departure time and you'll be none the wiser. Yuo could even have selected seats and booked the cook. All of which mean nothing.
the airline carrying you must have a ticket number against the booking.
there are some airlines you really do want to check to make sure they have ticket numbers... SQ, OZ, TG are three that come to mind.
Under what circumstances does is the e-ticket for some reason not correctly attached to all relevant booking across all carriers?
Now I'm not saying it can't happen. There may be a booking or PNR mismatch with e-ticket when you have schedule changes or the like (where the e-ticket must be re-issued), but having to check almost on a weekly basis (or daily?) that the e-ticket remains attached successfully to the PNR for all carriers (or simply the likes of SQ, OZ or TG) seems mind bogglingly obsessive and bordering on stupefyingly unnecessary.
I could maybe understand checking it upon the booking being initially completed. Maybe again whilst you are processing other booking elements, such as selecting seats. But having to do it on a regular basis seems ridiculous; not so much on the part of the customer being vigilant, but more on the part of it seems airlines actions or mistakes seem to necessitate it.
FWIW I have never done this on any booking on my watch. I have had schedule changes and e-ticket re-issues, but the e-ticket has never been detached from the bookings and thus I haven't a booking that hasn't fallen apart. Maybe I'm tempting fate, who knows.
If an airline's incompetence somehow results in their disconnecting an e-ticket from a PNR for any unknown reason which isn't raised to the customer, someone really deserves to be nailed painfully by their head to the wall with a long rusty nail. Literally. I could maybe "understand" TG (then again, maybe not, the "prostitute" of *A premium can do some strange things), possibly OZ, but to put this kind of imbecilic incompetence upon a carrier like SQ seems incomprehensible and reprehensible.