I did some testing with my new HD PENTAX-DA 55-300mm F4-5.8 ED WR lens. After importing the images in LR 2015.4 (latest version) on a mac (OSX 10.11.3) the lense info is not shown in any of the info panels.
Other lenses are recognized without any problems (35 2.8 Limited or even the old FA80-320).
For more information i already opened a posting at forums.adobe.com including sample RAW file and further description. https://forums.adobe.com/message/8443800#8443800
Sample Raw File: https://t.co/uyMLDQkaZO
I already created a lens correction profile by copying / editing the existing PENTAX (smc PENTAX-DA 55-300mm F4-5.8 ED) - RAW.lcp profile. With the copied profile the lense correction is working but the EXIF data for the lens is still missing in the EXIF pane. Other programs like Rawtherapee or DXO Optics show the correct lens.