Lotus made nothing on the bike, not the frame, nor a single component. They were a marketing company that had various companies in Asia build bikes for them, with the same parts everyone else was using during that time. Their decals appeared on some great bikes, I have three Lotus bikes right now myself.
Most of the components have date codes, which you can use to estimate the year of manufacture, if the parts are original. You can find more about date codes at the Vintage Trek site. Unfortunately, if someone stripped the parts off the frame, then the codes don't help. Almost every part bolted onto the frame will have a code on it.