Rooso --
I have to admit that I have not dug deeply into the dates, etc. of the transfer of the locomotives (and cars) from the N-C-O to the SP Mina - Keeler. Various records do exist.
The N-C-O remained as a separate corporate entity for years, even decades, after the conversion. The N-C-O operated separately until leased to the SP as of September 1, 1929. The property was transferred to the Central Pacific (still a separate entity) as of October 31, 1945; and the the N-C-O corporate entity ceased to exist as of March 19, 1946. [corporate history of the SP prepared by David Myrick and published in Dunscomb's
A Century of Southern Pacific Steam Locomotives.
I recall that while looking at N-C-O accounting records now in the collection of CSRM (notes are around here) that locomotive #22 was placed back on the account for locomotives when it was leased to the Southern Pacific. The SP then shopped the locomotive at Sparks and the list of work done filled up more than two record cards -- the work probably brought the locomotive to contemporary SP standards.
I have a copy of the SP's pocket-size book
Revised Classification and Assignment of Locomotives dated May 1, 1930. The first column gives the initials of the owning entity. Narrow gauge locomotives 11,12 and 14-17 are listed as C.P. and locomotives 1, 8, 9, 18 and 22 are listed as N.C.O. So for some reason the N-C-O ownership of the locomotives was not changed when they were moved to the Mina-Keeler line. Must have involved something like mortgage bonds that were outstanding.
N-C-O number 12 was renumbered 18 and N-C-O 14 became 1 because the SP already had locomotives with those numbers on its combined system. The numbers of number 8 and 9 were not changed because there was no duplication -- the earlier locomotives with these numbers were gone from the roster.
Brian Norden