Average annual value growth is independent of value. I am giving the OP's gun a better shake than you, but without inspection, we just do not know what is what. If a working well used NM3 was to sell in 1953, it would probably have been worth $20. A high condition NM3, according to early collector's guides would have sold for $50.
What would that gun have been worth 30 years ago? Let's say $200, or still an 8% AAGR. Sure the dollars are not there, but those excellent examples selling for $5000 to $10,000 are dragging the values of Fair & Poor condition guns up along with them.
I remember buying well worn Model 2 tip-ups for $75 to $100 in the late 1970s. You cannot find that same condition Model 2 for under 300 to $350. today. My view is that as prices on most sought after models get beyond what many collectors can afford, the value of lesser condition specimens rise faster than those high grade guns while slowing for those high priced examples. Anyway, my assessment is that accumulators and new collectors will continue to compete for those Good to Poor condition guns to fill holes as I did when I started out, pushing the prices yet higher.