So, looking back at my BattleTechnology magazines, it looks like they went into that level of detail three times (Brimstone in 0101, Wheel in 0201, and Mira in 0203). The feature was called "Worldbook", and though it appeared later as well, it never went into the detail of the first three. Each of the first three articles had about two-thirds to one page of raw data, followed by one to three pages of descriptive text. Mira was notable for its high level of just about everything being supported by a population just shy of 3 billion. Here's its "Armed Forces" data block (which I'm sure has been repudiated by TPTB long since):
"ARMED FORCES:
Defense Spending: 9.5% of GDP; Military Manpower Potential: 208,320,000 (7%); Aerospace Forces: Orbital Facilities: 3, Deep Space Facilities: 0, JumpShips: 12, DropShips: 60, AeroSpace Fighters: 95, Escorts: 8, Monitors: 4, Cruisers: 3; Battalions: Infantry: 529, Armor: 41, Air: 226, Mech: 9; MechWarrior Training Facilities: 6; Hiring Data: D/F/N"
The scenarios set on Mira in that issue were centered around a Capellan battalion that was "smuggled" on planet to conduct reconnaissance (which could almost be a link to the OP's original question... ::)). Somehow they avoided complete annihilation and were able to withdraw a remnant, but there's no discussion of how they avoided interdiction on the way to the jump point.
Wheels' similar data block is mostly zeroes, as the population listed there was only 2,400. They were given 6 DropShips, 12 AeroSpace Fighters and a "battalion-sized paramilitary militia" with four branches.
Brimstone split the difference, having a population of 12,675,693. Though given a Military Manpower Potential of 3,897,774 (35%) due to being a mining colony, it only had 3 DropShips, 6 AeroSpace Fighters and 3 Infantry Battalions.
I think Brimstone and Wheel were largely in line with what people generally think about the 3025 era, and being sparsely populated on the fringes of the Inner Sphere, they make sense to be that way. Mira might seem jarring, but it was a front line planet on the eve of the 4th Succession War. Issue 0203 was published in 1988, so I think it's reasonable to say that the whole population/size of militaries debate goes back at least that far.
To your point about "spelling out every planet" in that level of detail, the Worldbook articles had this kind of blurb appended to them:
"About Worldbook
Worldbook is a BattleTechnology feature drawn from the computer files of The Navigator's Guide to the Inner Sphere, the 32-volume compendium of explored worlds published by ComStar Press Interstellar, Terra. Mira was first printed in Volume 5, the Mirach Reach, and is reproduced here by permission of the publisher."