if you are either a noob or a relatively young former jock who went completely fallow for a period, i think you could drop a second in the 100 just doing the workouts. that's basically the initial fitness part. you were out of shape. you got more in shape. the hard part is you get under 12 or so. the curve rises and seasons were usually about chipping away another .3-.5. but then i would show up fairly fit from soccer, usually run one of my best times early-season, then usually finish with some more when we tapered, so the value of TF training was marginal.
anyhow, point being if you dropped a second you probably started slow or are just getting in shape, where you get bigger benefits. enjoy the moment but that probably usually just catches you up to the back of the competitive pack.
kind of like 5 minute mile. you can probably take a kid off the street for XC, and if they are a willing worker, shave minutes off their mile time and get them around 20 5k and 5 mile. from there is then a mix of talent and chiseling away a dozen seconds a season.