never heard of a Sorrento. are you sure that's not the name of the grower's company? Here is a site with a lot of varieties listed.
http://www.citrusvariety.ucr.edu/citrus/lemons.html
is there a difference in the amount of sun they are getting? Lemons love full sun and shade could slow their growth, especially close to the coast. close to the coast some varieties will be especially slow growing.

The term Sorrento, I believe, is referring to the area it is grown. I also made the Costco purchase, back in spring of 2007. I chose the variety "Primofiore" and hope to one day make the limoncello. It was planted amongst our other lemons, and we have not seen much growth since. A few flowers appeared and dropped last spring. I am guessing that it will take a few years for production to "kick in". I have a Lisbon nearby with same MO purchased from Thermal Plaza. At that time we purchased a truckload of citrus from Thermal and YoungÂs nurseries, but only the Lisbon lemon is not doing much. But on the other hand, it took four years in the ground and a few years spent in the container for our limes to get going.

The Sorrento lemon is mentioned in Julia MortonÂs book "Fruits of Warm Climates".
'Femminello Ovale'Âone of the oldest Italian varieties; short-elliptic with low, blunt nipple; slightly necked or rounded at base; of medium size; peel yellow, finely pitted, medium-smooth, medium-thick, tightly clinging; pulp in about 10 segments, tender, juicy, very acid, of excellent quality, with few, mostly undeveloped, seeds. Fruits all year but mainly in late winter and spring; ships and stores well. The tree is almost thornless, medium-to very-vigorous, but highly susceptible to mal secco disease. This is the leading cultivar in Italy, accounting for 3/4 of the total lemon production, and 1/5 of the crop is processed as single-strength juice.

UCR also has the C. femminello ovale in its collection. It is located at "other lemons and hybrids". When looking at their lemons, only the Citrus femminello will pull up with info, but the "femminello ovale" is on the list without info link. It doesn't seem to appear in the CCPP; just the Variety Collection.

It appears that patience will be required for these lemons; another year or two. I cannot locate the nursery tag, so do not know if the grower was mentioned on the Costco tag.

Pam

Here is a link that might be useful: European Citrus Page