My understanding is early cars originally came with 4 keys. 2 red main ignition keys with badges on, 1 red valet key no badge that could not open boot or glove box and a brown master key that can be used to program new ignition keys. Also an alarm fob. Later cars had central locking built into keys.
Not all GTVs have an alarm. I believe it was standard in the UK, but not even an option for cars sold here in Sweden.
My Phase 1 car have one brownish master key and two red keys, one with a badge and one without. I have never tried if the one without the badge is only a valet key, I will check. There are only three keys programmed in the immobilizer box, so there have never been a fourth key.
A phase 1 car should also have a code card with a mechanical code (used for grinding of new keys) and an electronic code for emergency start if the immobilizer fails. The electronic code is derived from the transponder logic in the master key.
If you don't have the master key it's no worries. You only need it if you want to program new keys in the immobilizer system, but you can still get more keys if you clone
the transponder of one of your existing keys. Any good car locksmith have the equipment to do this.
If you loose all your keys you can still be saved. It is possible to extract the transponder data for all programmed keys from the immobilizer box, at least if you have the yellow box (606 22 718). From the same box you can also retrieve the emergency start code, although the algorithm between master key transponder logic and code is not public, so you need the software ICC (Immo Code Calculator) to get it.
It is a good idea to take a sharp photo of one of your keys. From that it is possible to get the mechanical code and you have a backup for that if you loose all the keys.