Two more points to bear in mind when looking at this stamp (and it certainly
looks like the reprint):
- Nabha was a fairly small State. Under the terms of the 1885 Postal Convention, these overprinted stamps could be used to addresses throughout India, but 1 Rupee represented 16 times the basic letter rate, or about 8 times the registered letter rate. As these curved overprints were replaced after a few months anyway, usage must have been microscopic.
- There was no income tax: States like Nabha derived most of their income from various other dues and taxes, particularly Court fees, for which a rupee stamp might well have been used.
That said, Gibbons (and market) prices for used high values of the Convention States, like Nabha, appear to be right out of whack with reality. Gibbons prices these Edward VII 1 Rupee stamps of Patiala - a much bigger State than Nabha, but still only a State -

at 80p each, against 70p each for the all-India version, without the overprint. I simply don't believe that the Patiala government had
that much need to post articles costing 4 Rupees.