Lenses with fewer elements (when discussing older lenses but this is not as relevant to new designs because coatings are so much better today) and, more importantly better coatings, will potentially give higher contrast. Zeiss T* coatings were always excellent and I think this accounts for their high contrast, especially during the period the OP is discussing. Flare (glare) kills contrast.
I'm not sure how much emphasis we should be placing on coatings compared to lens design. I have and use many coated lenses, I don't use the term single coated because many have more than one coating layer but are not the balanced Multi Coatings we know today.
I have an early 1950's T coated 150mm f4.5 CZJ Tessar, the coatings are excellent, no hint of flare even where MC modern zooms are next to useless, the downside is the blue colour bias. But like other companies CZJ overcame this with balanced coatings in the 1960's, a CZJ example if the Flekton which became the PAncolar with the newer coatings, Woigtlander introduced the Color Skopar etc.. Now I have 3 other T coated CZJ lenses and along with the 150mm Tessar all have excellent contrast and sharpness but the later coatings are definitely better for colour work.
Now in the early 90's when I still shot a lot of 35mm I used an M3 Leica, f2 50mm Summicron, as well as a few Pentax SLR's. I had Super-Takumars and SMC Takumars and frankly there was no discernible difference in practical use with the lenses I was using, there was probably a measurable difference in a lab and particularly with zooms.
Overall contrast was negligibly different between my 50mm Summicron and 55mm Super/SMC Takumars, micro contrasts was more apparent with the Pentax lenses but it was obvious the Summicron had something different more tonality and a different type of resolution. I saw the same with the CZJ 35mm lenses of a friends Exakta VX1000, he used a 35mm Flektagon, 50mm Pancolar, and a 135mm Sonnar, these produced some of the best 35mm negatives/prints I've seen.
My Summicron was mainly used for B&W work the few times I shot colour with it the results were superb, definitely a slight difference compared to the Pentax lenses or friends Nikkors, that difference was apparent to non photographer friends.
Perhaps Crawly's 1960 terms are worth quoting:
" Sharpness "-the overall impression of a print or projected image, measured scientifically as " Acutance ", seen from normal viewing distance.
" Definition "-the extent to which fine detail is recognisably rendered in a print, etc. When acutance of fine detail is good, then definition is good.
" Acutance "-the contrast at the edge of significant detail, a scientific measurement of the density gradient at that point.
" Resolving Power "-the scientific measurement of the actual fineness of detail recordable by a lens, film, or developer, or any combination of these three.
While it's just nuances in the terms in practice design criteria are different particularly between German and Japanese optical companies.
Ian