Is the C/Y 50 1.4 (MM)Planar the same optical formula as the new ones offered is Nikon F mount and EOS mount?
Datasheets for both lenses are on the Zeiss site.
The MFT curves are different and the cutaway pictues are similar but very slightly different.
Yashica/Contax (Rollei?)
http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/Planar1.4_50mm_yashica_e/$File/Planar1.4_50mm_yashica_e.pdf
ZF
http://www.zeiss.com/C12571FF00438F7A/0/4DBF8F5EBA9BB366C12576930030E0A3/$file/planar_14_50_en.pdf