Don, those "earlier" lamps are known as "P700" and took a more typical (for the time) headlamp bulb. Original "PL700" with the PL shield rather than the round LUCAS center) took a Type A headlamp bulb.
For whatever it's worth, PL700 lamps are not shown in my Lucas Master Catalogue 1945-60, but the P700 lamps are shown. Also, if you look at any number of factory publicity photos of TR2, TR3 and early TR4, it is the P700 as pictured above that you see.
Finally, even originals weren't always the best. I bought some NOS P700s back in the mid-1970s (I worked briefly in an ex-Bap-Geon store, and -- honest to goodness, there was a pallet full of NOS P700s!). Optically, they were fine, but some of the tri-pod bars weren't aligned very well inside!