There is an odd pair of sites called something like "3rd party lens megasite" and "medium format megasite" with tons of info, but it's design appears to be from the child hood of www and many pages are only available occasionally for some reason. Anyway, with the usual reservation for the accurasy of something you find on the web, there is a list there of lenses tested for flare by a photomagazine in the 70's:
"Flare Results sorted by % flare (hi to lo), f/l, f/stop
Lens f/l f/stop flare %
71) Zuiko 70 2 4.5
70) Miranda 135 2.8 4
69) Nikkor 135 2.8 4
68) Summar RF 50 2 3
67) Topcor 25 3.5 2.9
66) Nikkor 105 2.5 2.9
65) Miranda 105 2.8 2.9
64) Elmar 90 4 2.8
63) Miranda 35 2.8 2.5
62) Nikkor 35 2.8 2.5
61) Canon FD 300 5.6 2.24
60) Topcor 200 5.6 2.1
59) Elmarit 90 2.8 2
58) Rokkor 21 2.8 1.9
57) Takumar SMC 150 4 1.9
56) Canon FD 100 2.8 1.89
55) Zeiss Distagon 40 4 1.86
54) Miranda 28 2.8 1.85
53) Leitz S. Angulon 21 3.4 1.8
52) Elmar RF 50 3.5 1.8
51) Zeiss Sonnar 250 5.6 1.7
50) Summicron RF 35 2 1.67
49) Summicron RF 50 2 1.67
48) Mamiya Sekor ES 55 1.8 1.66
47) Takumar SMC 135 3.5 1.63
46) Takumar 28 3.5 1.55
45) Zeiss Sonnar 150 4 1.54
44) Rokkor 100 2.5 1.52
43) Zuiko 20 3.5 1.5
42) Mamiya Sekor 100 3.5 1.48
41) Canon FD 24 2.8 1.42
40) Zuiko 40 1.4 1.42
39) Summicron R 35 2 1.4
38) Zuiko 38 2.8 1.4
37) Zuiko G Auto-S (OM-1) 50 1.4 1.39
36) Zeiss Distagon 50 4 1.37
35) Canon FD 35 2 1.29
34) Takumar 55 1.8 1.28
33) Takumar SMC 105 2.8 1.25
32) Zuiko 42 1.2 1.1
31) Summicron M 90 2 1.1
30) EBC Fujinon 50 1.4 1.04
29) Elmarit 28 2.8 1
28) Miranda 50 1.8 1
27) Nikkor 50 1.8 1
26) Takumar SMC 85 1.9 1
25) Nikkor 24 2.8 0.98
24) Hexanon 85 1.8 0.98
23) Zeiss Planar 80 2.8 0.96
22) Takumar SMC 135 2.5 0.92
21) Takumar SMC 28 3.5 0.9
20) Summilux 50 1.4 0.9
19) Takumar 50 1.4 0.9
18) Summicron R 90 2 0.9
17) Topcor 100 2.8 0.9
16) Canon FD 50 1.4 0.88
15) Hexanon 135 3.2 0.88
14) Hexanon 52 1.8 0.85
13) Rokkor 35 1.8 0.81
12) Zuiko G FTL 50 1.4 0.8
11) Meyer Oreston 50 1.8 0.8
10) Takumar 35 3.5 0.73
9) Canon FD 50 1.8 0.73
8) Summicron R 50 2 0.7
7) Hexanon 57 1.2 0.625
6) Takumar SMC 35 3.5 0.62
5) Topcor 35 2.8 0.6
4) Singlet, Pl, Cnvx in Barrel 100 4 0.6
3) Takumar SMC 55 1.8 0.58
2) Noctilux 50 1.2 0.56
1) Takumar SMC 50 1.4 0.47
Source: Popular Photography December 1973 p.240
Flare tested on-axis, without lens hood, and
wide open unless otherwise state…
End of Page"
Here is the link
http://medfmt.8k.com/mf/flare2.txt, though at this moment it does not work.
It is worth noticing that among the ten lenses with least flare there are four Takumar lenses, three with SMC (50/1.4 being the best of all, plus the 55/1.8 and 35/3.5), the forth is the 35/3.5 without mulitcoating (or at least without the "smc")! A total dominance over other brands in this test.
So for the 35/3.5 the flare decreased from 0.73 to 0.62%. Not a hugh difference! Perhaps this non-SMC was a late super-takumar with some (S)MC on it, as you speculate?
Other pairs of SMC non-SMC Takumars in the list are
lens - non-SMC flare - SMC flare
50/1.4 - 0.9% - 0.47%
55/1.8 - 1.28% -0.58%
35/3.5 - 0.73% - 0.62%
28/3.5 - 1.55% % - 0.9%
So there were quite some redcution in the flare between non-SMC and SMC versions of the 28, 50 and 55mm lenses.
You notice of course that Canon has only one lens among the 10 best (nr 9 a 50mm) and Nikon not one (their best is a 50mm at the 25th position).
This list kind of support what you here that SMC did a difference and that Pentax was the leading lens manufacturer at this time...
Would be interresting to read the whole paper and see how they commented it back then.