Well, that matter is inherently a something to debate and, given the constraints of scale and style, there could be no "100% one and only true and proper way", but IMHO htere could be certain "tendencies".
In regards to the drawing in question - the green arrow points to place where double-black line is perfectly acceptable to me as is seems to be unavoidable and there seems to be no good alternative to it; the orange ones point to two places where I think it could be avoided, but I wouldn't make a big deal out of it, and the red ones point to places which I really
For example, it seems to me that the 'thing' immediately aft of the turret is something like cover over the engine that extends over the hull - and to me it would look better if it was done with two parallel black lines with grey (color) line between them, instead of that mix. Same situation at the very back of the vehicle.
My rationale is that what we're doing are not, strictly speaking, technical plans, but representations of various vehicles made using certain conventions, which occasionaly deliberately introduce certain inaccuracies
in the interest of clarity and "clean-ness" of the drawing.
Obvious example of that - in SB scale - is the rule that makes all catwalks, stairways and the like are shown in 3-pixel format (contour-color-contour).
P.S. Yeah, I agree, it wouldn't be bad if there were several few more black pixels on MBT-70's tracks.
P.P.S. Earlier on this page I expressed similar concerns about double-black lines on Yqueleden's drawings. Here's a small sample I understand the idea of "clarity" and "clean-ness" comparing the original drawing (top) and "how it can be done otherwise in my humble opinion" (bottom).