For collectors of the Estes "K" series kits this designator ended with the K-58 Demon kit.
By the time of the 1974 Estes catalog new kits were being released with the "12XX" code and eventually all the remaining "K" kits would be re-coded with the 12XX designation. For example, the afore mentioned K-58 Demon became 1258.
However, there was one less known Estes kit that received the designation K-59. That was named SPEV.
This kit only appeared in the Estes Model Rocket News and never in any catalogs.
First appearance was the July 1972 issue (V12 N3).
It was a mail-order only model.
The model seemed to be made up of parts from discontinued kits (Little Joe II, Thor Agena-B).
Later it was found out that SPEV was short for "Spare Parts Elimination Vehicle".
Or, at least that's what folks said.
The model appeared again in the December 1972 MRN (V12 N4).
The SPEV's final appearance was the May 1973 issue of MRN (V13 N1) where the SPEV was noted as being a free kit with a mail order purchase of $15.00 or more (That was a lot of money back then).
So, the SPEV faded from the memory of rocketeers.
By the time of eBay SPEV kits started showing up infrequently and often went for big $$$.
I had sometimes thought of getting a SPEV but it never really took hold with me. There were several clone kits made of the SPEV by different hobbyists/manufacturers (The latest one being the recently discontinued Semroc version).
I picked up a few of the Semroc versions and figured that was enough.
Then, the opportunity to get an original Estes K-59 SPEV kit came to my attention.
I figured "Why not" and was able to obtain the model.
The model was in very good condition with no damage to any of the parts and only minor wear to the packaging.
Attached are pictures of the kit along with scans of the two MRN pages showing the SPEV.