We talked some about the 20-lire coin on the Italian forum, and I read remembered some more, and came away with the following:
!) The aluminum-bronze 20-lire of 1957-2001 did indeed die a natural death, done in by inflation. (Although it suffered from other disabilities along the way.) Pro forma quantities only were coined after 1992.)
2) During 1966-69, the coins in common circulation—in Napoli and the surrounding area, anyway—were the 5-, 10-, 50-, and 100-lire, with the 20-lire being somewhat less common, and the 500-lire, common at first, rapidly disappearing in favor of a paper note. (“Caravels” were seen much more often than “Centennials.”) The 1-lira and 2-lire were completely out of circulation. Very, very occasionally a Vatican City 100-lire from the ‘50s would show up. (American coins—mostly older than those circulating at home—circulated within the military community, and still had some currency locally—especially Kennedy half-dollars, which were
always accepted.
3) In 1966-67 when I first saw them, the 20-lire pieces of 1957-58 (the only dates I saw) were worn and had clearly seen hard use.
4) In 1985, on a brief visit, the coins I saw in common circulation—in Napoli and the surrounding area, anyway—were the 50-, 100-, 200, and (bimetallic) 500-lire. The 10-lire was still circulating, but seemed much less common. I never saw a 5- or a 20-lire.
5) Until the 1977 advent of the aluminum-bronze 200-lire, the 20-lire coin was of singular appearance within the Italian series, and was often removed from circulation by collectors, accumulators and souvenir-hunters.
6) The rumors of the presence of gold in the 20-lire added to the pressure on the coin. Might that have been especially so during the gold frenzy of 1979-80? Maybe so. Heck, probably so. But that dynamic seems unlikely to have made any sort of disabling impact on the 20-lire’s circulating presence. And certainly not, with the series’ production peak in in 1980-81.
7) A tantalizing mention was made of Italian soldiers being paid with freshly-struck 20-lire coins about 1979 or 1980, but the reference was not confined to 20-lire coins, and despite the prompt, no other posts mentioned anything similar.
#8 Finally, another disability afflicting the 20-lire was repeatedly mention. That is, the 20-lire, once inflation moved the cost of things beyond its specific price-points (where the coins were individually useful for exact payments or for making exact change), the more flexible 10-lire tended to crowd them out.

v.