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Btw. what means "dual control"? Does it mean there are two different keys which unlock the lock? Or does it mean the lock has two bolt stumps like e.g. in the SMP lock?

Typically requires two keys or codes. Regarding code locks: One is called manager code and the other is user code. User code doesn't work unless the manager code is input first.

In mechanical key locks it is like a banks safety deposit boxes: requires two keys to open and usually the other (manager) key blocks the keyway of the other lock.

Btw. this is what is written about that in 550 part 1:

7.6 Locks
7.6.1 Type
Lock shall be of dual control type. ...
7.6.2 Levers
... Each lever shall have two slots for the passage of main and auxiliary bolt pins. ...

I can't find much about Indian safe locks online. Found only two photos of closed safe locks which have a casing constructed similar to a Chubb 6K75, one key hole and one set of keys. It does not necessarily mean that these locks I found are really locks conforming to IS 550 part 1.

Steelage used to do a lot of dual control locks, over here they are quite a rarity, normally for older bank safes or grille gates that were only originally made with a single keyhole, but for the banks needed to have dual control. another way used by banks to achieve dual control on a single keyhole was to fit a locking escutcheon.

Non compulsory dual control where it can be left on 1 key to lock/unlock only, or compulsory dual control, similar to a safe deposit locks operation where both keys have to be used together to open.
a steelage, a chatwood and some chubbs.

wouldn't let me upload the steelage picture, but similar design to the chubb locks.

The Indian standard specifies 8 levers. I imagine that they would have written it differently if there were two lever packs like in a bank deposit lock.

The dual "bolt pins" could mean something like in the second Chubb lock or the higher security Milner locks with up to three bolt stumps.