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Hey does anybody know were the STC's specific towards a particular aspect of technology, like military tech, or did it include everything from like sustainable atmosphere to food harvesting?

They do pretty much everything.
The people who designed them apparently did so to provide a colony with everything it could need, and make sure the tech was easy enough that anybody in said colony can build it.

In earlier novels, they seem to have been for specific things, like the Iron Men STC Gaunt destroyed.

I guess it depends which source you look at. As far as Games Workshop is concerned, the following is an excerpt from the rather extensive Rhino article that appeared in White Dwarf #269:

"[...] However, all this was to change soon after the colonisation and exploration of Mars, with the development of the Standard Template Construct (STC) system. The exact origins of the STC system have been lost in the thousands of years since its first discovery, but tis impact has ramifications that still resound in the 41st Millennium. The sheer versatility of the STC system enabled the earliest colonists to simply input their needs and the STC system would design the most practical and robust solution to meet those requirements, be it a vehicle, shelter or any other item the colonists desired.

The STC allowed the early colonists to create all manner of useful equipment from locally available materials and fuel them with whatever resources were to hand. As time passed, refinements were introduced into the system and it is said that many of the earliest STCs could in fact learn and self-evolve. STCs became more and more efficient, and with their perfection Mankind's expansion into space leapt forwards as starships became capable of reaching further and further into the galaxy.

[...] Countless designs were lost and many of the STC systems were damaged beyond repair. By the time the wars subsided and Mankind had been united under the banner of the newly-revealed Emperor, the vast majority of STC systems had been destroyed and their priceless knowledge forgotten. [...]

[...] Hard copies of schematics and designs created by STC systems have lasted longer than the STCs themselves and have become the holy grail of the Adeptus Mechanicus, who eagerly seize on any scrap of information that might lead to the discovery of even the tiniest fragment of an STC's output. Over the millennia, scattered pieces of STC lore have been recovered and ancient designs have slowly been reincorporated into the Imperial inventory. [...]"

Gaunts Ghosts (IIRC) specifically mentions a regiment that found an STC for making knives (and bayonets, swords, or any other typical knife like item) and were rewarded with a Discharge from the IG and a new home planet to colonize.

STC's were designed to contain pretty much everything. The ones survived are corrupted, broken, etc. therefore stuck with a single or very few items. Thus an undamaged STC is considered as a Holy Grail for Adeptus Mechanicus.