I've used a few different resources including some things here on Lernu, Duolingo, and "lern.esperanto.com" and between at least these three places I've seen compound nouns handled slightly differently.

In one instance a noun like "work bench" would be "laborotablo," while in another place I'd see the same (work bench) translated as "labortablo" (that is, without the -o on the end of the first noun in the compound). And I think I've seen this happen inconsistently even within the same resource.

What is, if there even is, the "official" rule when it comes to compound nouns and that -o on the end of the first noun?

IMO, for whatever it's worth, keeping the -o ending of the first noun in the compound feels cumbersome and unnecessary (at least, unnecessary within the context of compound nouns). Also, can anyone reveal to me - if the first noun in a compound noun DOES retain that -o ending, is it something that is still definitely pronounced as I'd expect? In my mind, I can picture the "real" word being laborotablo but folks speaking quickly saying just labortablo. (Only the -o on the very end of the word is even really functional, right?)

The meaning of a noun may be amplified with a prepositional phrase, nearly always following the noun:
minejo de oro = gold mine
forko por fojno = fork for hay
leviĝo de la suno = rising of the sun

Such structures can be converted to compound words by attaching the object of the preposition (with or without its final -o) as a prefix to the noun and omitting the preposition. The -o is usually omitted unless its presence eases pronunciation (in the opinion of the speaker).
or(o)minejo = gold mine
fojn(o)forko = hay fork
sun(o)leviĝo = sunrise

More examples:
sofolito = sofa bed
monsumo = sum of money
skribotablo = writing table
radiodissendo = radio broadcast
Esperanto-klubo = Esperanto club
dormsako = sleeping bag
vinglaso = wineglass

http://pages.ucsd.edu/~dkjordan/eo/colloq/colloq04...

josxuo:What is, if there even is, the "official" rule when it comes to compound nouns and that -o on the end of the first noun?

There is no official rule. You can keep the -o or omit it and it's not wrong either way. As the sources you cited said, the -o is usually omitted unless it eases pronunciation. for instance, consider "water bottle."
"Akvbotelo" is hard to pronounce. Keeping the -o and saying "akvobotelo" is much easier.