Here's a visual overview of the TOS Constitution class variants:
It was a modified TOS Constitution Polar Lights instructions with highlights/red circles for each version's differences. There are decal specifics on the bottom.
Starting with the 1st Pilot:
No lights (all painted on)
Bridge: double high
Saucer top: gray bands painted near port & starboard edge
Saucer bottom: NCC on the inside, No Lower Saucer Dome nipple (phasor)
Impulse engines: black rectangular vents
Secondary hull: Large deflector dish, Smooth Shuttlebay Doors
Nacelles: Nacelle spikes,No ball on nacelle end cap.
2nd Pilot differences from 1st Pilot:
Bridge: several painted-on windows removed, light panels added in front and on sides.
Saucer top: nav lights added, black bands painted near port & starboard edge, painted black & white areas added near bow edge, four light panels added. The port & aft light panel was just painted-on and is not an actual light panel.
Saucer rim: centermost bow port changed to nav light, some windows added.
Saucer bottom: nav light & 2 portholes added near edge on each side, at 10 and 2 o'clock positions.
Impulse engines: black rectangular vents painted over with hull color, eight small round black vents painted on.
Secondary hull: strobe light added on aft flank, rearmost round porthole moved from left side of two rectangular ones to right side.
Nacelles: black "grille" pattern painted on rear nacelle end caps.
Registry markings were previously painted-on, now changed to decals.
Mirror differences from 2nd Pilot:
Large Terran Empire insignia on top of nacelles and bottom of secondary hull
Medium Terran Empire insignia on top front of saucer
Small Terran Empire insignia on shuttlebay hangar doors
USS --> ISS
Production Series differences from 2nd Pilot:
Bridge: bottom half chopped off, light panels removed, a red “beacon” added on each side. Some portholes added on B&C decks.
Saucer top: black bands and most other painted-on markings removed, a round light panel added near bow edge, rib added on "linear accelerator" and both painted a darker gray.
Saucer rim: Some portholes added, bow nav light replaced by light panel
Saucer bottom: nav lights moved to 9 and 3 o'clock position, some portholes added, "nipple with phaser turret" added below sensor dome, NCC on the outside.
Impulse engines: painted darker gray, round vents removed, original rectangular vents again painted black, texture wraps added on both ends of impulse deck.
Dorsal: some windows/portholes moved/added, dorsal painted same as rest of hull instead of the earlier bluish reflective color, with a darker region on both leading & receding edge.
Secondary hull: red "beacon" & green portholes added on top, some windows/portholes added, deflector dish diameter reduced, "observation booth" added under cowling above hangar bay doors.
Nacelle pylons: four dark gray. brick-pattern inserts placed in slots.
Nacelles: solid wood "power nodules" with spikes replaced with frosted plexi-glass domes with inner surface painted transparent orange, plus motorized vanes and blinking Christmas lights added behind the dome. Ribs and aluminum grille added in "trenches" along inboard flanks of nacelles and trench painted darker gray., patterned slabs added inside "intercooler loops" at rear, small slabs added in front of intercooler loops, black painted grille removed from end caps and light gray. spheres added. Typeface used for registry markings changed, weathering added.
I plan to incorporate various configurations of my Connie's.