If it’s wired in mineral there is a good chance it’s a 3 wire, no detection is also a give away, and I think the panel has been modified to run this old job.
You don’t say whether the end of lines are monitored , so your wiring could be teed and spurred , don’t assume that an end of line is a monitored radial.
If it not a 3 wire, it might be a conversion to a hybrid semi monitored system, years ago we would have a 24v feed to each detector and a reference core.
They obviously know something that you don’t, and who says they are going to comply, do yourself a favour and unless you know without a doubt how this building is wired etc, quote correctly to cover you, there is no point in carrying on with this unless you have an eggs for eggs specification.
Remember Salesmen who get it wrong , leave it to the fitters , commissioning guys , they can afford to lose money , so you might as well go to the cash point and give your proposed client some money now.