So many bikes of the types we are interested in have lost identifying marks. It does become necessary to do this kind of cross-referencing to identify what it is that you have found.
Once these basics are complete, hopefully we can get into some specifics within brands that will help identify years of manufacture more closely. For example, nearly all manufacturers changed their metal headbadges to foil stickers at some point in the later years of American production or as Taiwan or Chinese production begins. My own pile of Columbia frames shows a few different styles of headbadges as well as frame construction.
Some little bits of knowledge I've picked up over the years:
Schwinn was unique in their "Electro-forged" frame construction that produced the smooth curves of the tubes meeting the head tube.
Other joints made on the bike may be rough, but the frame head is always smooth and rounded. Some of the 10-speed bikes of the classic era, however used Japanese frames (Panasonic built) and these would be lugged frames (typically LeTour and some World or Traveler models).
Columbia made bicycles other than lightweights often feature that distinct rear hoop behind the seat post, as shown in the above picture. The only other example I know of for this arched top chainstay design is on the Vista bicycles. You can see that design on a Vista Torino 500 20" bike on my site: http://www.bareiss.net/bikesale.html
Ross bicycles (Chain Bicycle Co. of NY) often use a twin top tube design. Most of the boys 20" models used this, except the chopper-style Apollos. This design extends the top chainstays all the way to the headtube, and a second pair of cantilever bars runs parallel below these. Multi speed models up to '73 may have a shifter bracket welded under the top tubes. Ross Barracudas are an example of this style.
Columbia used different brand hubs on the same model bikes. I have had several ladies Columbia Sports 3's, mostly with Sturmey Archer AW hubs, but 1 had a Shimano coaster 3 hub. All these bikes appeared to be 100% original.
Huffy built bikes for the Grants department stores. I have examples of identical components and frame designs on Huffy-badged and Grants-badged bicycles. Huffy at one time also sold "The Wheel" and other "rail" type 20" chopper bicycles to Sears. These and the more common Murray bikes may be badged as Free Spirits.
Murray built many bikes that ended up with other brand names. A friend owns a totally original 1959 26" men's cruiser badged as a "Fleetwing" with Murray "M" decals on the seat post and Cleveland Welding marks on the bike in various places.
Coaster hubs: this is better documented in other places, but a quick summary of the common Bendix hubs is always helpful. By 1982, the Bendix hubs seem to have been replaced with Shimano coasters. Bendix 76 hubs are used from late 76 on (1977 up models). Bendix 70 hubs appear in late 1970 for 1971 to 76 models. Prior to that, there are different versions of the Red Band hub. The RB2 model was in use from 1966 or 67 to 1970. There is also a RB "Junior" hub made concurrently to these for children's bikes, but I do not have firm production dates on these.
When dealing with any "unknown" bike, it's always helpful to take apart major assemblies and search for casting info or engraved dates or manufacturer codes. For example, a Schwinn one-piece crank will have a date code forged right into it. Early models (mid 50's or earlier) may only say "AS&CO". Later ones, like the crank on my workshop table right now give the date code this way: SA 6 69 , a June 1969 crank. The SA as I understand it means "Schwinn Ashtabula", Ashtabula being the company that actually did the forgings for Schwinn for their cranks, forks, and stems. Likewise, with many components, date codes can be found or decoded to narrow down the build date of the bicycle. Handlebars, cranks, forks, pedals, tires, hubs, stems, rims, and sometimes even bearings can give up date codes to help determine what it is you have found.
This looks like it will be a valuable tool to the forum. Hope lots of good info lands here. We're off to a good start.