I went through some of my old paper references. The .38 Long was introduced in 1875. It was avalable as both a heeled bullet with a 0.879 case (130 gr bullet 15 gr BP 770 fps) and as an internally lubed bullet with a 1.017" case (150 gr bullet 18 grain BP 770 fps) both with the same overall length (1.324").
The 1878 UMC catalog lists the 38 Short adapted to Colt's B.L. Police Revolver and the 38 Long adapted to Colt's Navy Revolver. Both are heeled, C.F. cartridges. The 38 short had a 0.765" case.
My guess is that only Colt produced the internally lubed bullet and UMC produced the heeled bullet, hence the differentiation between the .38 Long and .38 Long (Colt's). This would fit in with Colt and the .41 cartridge used in the Thunderer. It was rifled for the heeled cartridge, but Colt stopped production of the heeled cartridge and only produced the internally lubed version for it.
Frisco,
Yes that is correct, 1875 for the .38 Long, and as you said it was in both flavors. However Colt's was converting Model '51s and '61s to .38 Colt in 1873. The Navy sent over 3,000 of them to be converted. I believe those were the .88" length case.
People are easily confused by markings and not paying attention (or knowing the specifications of things like chambers). Colt's was bad about marking everything .38 Colt no matter the actual cartridge. Shorter .88" cases, true 1.03 Long Colt cases, heeled bullets of Ø.375 diameter and internal bullets of Ø.358. They also had Rimfire cartridges and Central Fire cartridges. All were marked .38 Colt from what I have read. I saw a .38 Rimfire once but I can't remember for the life of me how it was marked for the cartridge type. If I had to guess I would say it simply was stamped. .38 Colt. I'll look at my conversion book later maybe it has a picture of one.
~Mako