Here are all hull numbers I could find in CLs, CAs and BCs, plus the strength numbers before the war:
Light cruisers
- 1535 (refit): HMS Casey (CL-01)
- 1649: HMS Unconquered (CL-16)
- ??: HMS Trenchant (CL-19) [could be a Courageous, was in service in 1887]
- ~1800: Courageous class, 62 built
- 1820: HMS Fearless (CL-56)
- 1856: Apollo class, 132 built (+52 in Flight IV)
- ??: HMS Perseus (CL-92)
- 1871: Talisman class, 16 built
- 1876: Illustrious class, 26 built
- 1902: Valiant class, 83 built
Heavy cruisers
- 1590: formerly HMS Nike (BC-09, CA-103; I assume out of order)
- 1794: Warrior class, 46 built
- 1809: Truncheon class, 77 built
- 1842: HMS War Maiden (CA-39), Warrior-class
- 1851: Prince Consort class, 175 built
- ??: HMS Broadsword (CA-47), Prince Consort-class, 8 of which modified in 1873 or later as Broadsword class
- 1851: Crusader class, 25 built
- 1893: Star Knight class, 77 built
- ??: HMS Warlock (CA-277)
- 1901: HMS Fearless (CA-286)
(there are 10x more Prince Consort ships than there were princes & princesses consort)
These numbers indicate that by 1844, the RMN must have had ~50 light cruisers and ~30 heavy cruisers in service. Along with 11 BBs, 11 DNs and 3 SDs, plus some BCs, that seems like a respectable force for a single system polity with extra-territorial patrol needs, but nowhere sufficient to halt the PRH advance.
During the build up, they must have built 250 CLs and 300 CAs. So it could easily go from CA-39 in 1842 to CA-286 in 1901, reaching something like CA-350 shortly before the war, with the Star Knights being built for years into it. That also seems completely achievable, especially considering they were building hundreds of wallers at the same time.
Now the BCs:
Battlecruisers
- 1460: HMS Nike (BC-09, later CA-103)
- 1590: HMS Nike (BC-01, count restarted)
- 1786: Redoubtable class, 118 built
- 1863: Homer class, 86 built
- 1896: Reliant class, 95 built
- 1904: HMS Nike (BC-413)
Even assuming HMS Nike was the 95th and last ever Reliant built, that's only 298 BCs in the 1800s. With a hull number of BC-413, we're missing 115 ships. Could the RMN have built that many in the 1600s and 1700s? That seems unlikely for a fleet that had built less than 50 CLs and CAs. In 1844, it would mean over half the fleet units were BCs.
It's not impossible, given that 118 Redoubtables, 46 Warriors and 62 Courageous, which are roughly from the same time period (1785-1800). But it's a stretch, so to me, it seems far more likely that there was one more class of BCs in the 1800 that wasn't listed.
Unless the hull numbers are not sequential?