Isn't tN just Time Frame?
The .inx files (compiled .ini / .inf or WHY) break from - to time frames as being individual animations from the whole. Like 0 - 35 = Stand, 36 - 48 is Walk, 49 - 60 is Run etc.
I would expect animation time frames between 0 and 160 (in your example) will be automated "tweening" where the command lines effectively create a "key frame", but clearly only for a single point / joint.