The Fw 190 D-12 never went into production. Three 'versuch' (prototype is an approximate translation) aircraft were built. The 'Technical Directive of the Reichsmarschall No.4' dated 11 March 1945 is explicit.
"5. The variants Fw 190 D-12 and D-13 will be merged, provided this will actually result in a reduction in the number of variants. The number of variants of the Ta 152 will be reduced to a minimum."
As for the D-13, there is OKL General Quartiermeister document from April 1945, reporting on the previous month, which states that by 7 April 1945 there were two D-13s in service with the Luftwaffe.
Circumstantial evidence like the highest 'werknummer' (836017) found on an extant aircraft (Franz Gotz's 'Yellow 10' of JG 26, surrendered at Flensburg) suggests that at least seventeen D-13s were in fact completed.
There is little certain about production taking place during the cataclysm of Germany's final defeat.
Cheers
Steve