PL-L 55w... how many lumens REALLY?

There have been threads here and there about these alternatives to 2' T5-HO called PL-L, Dulux-L, etc. which boasts a staggering 4800 lumens per bulb. HTGsupply claims 5000 lumens per bulb! For the uninformed these are like 4' T5 tubes, but they are curved back on itself to fit into a 2' length. They are technically CFL's because they are bent.

However, these lumen specifications seem to be different for different 55W PL-L type bulbs. For instance, here's the exact same PL-L bulb made by Philips which is listed at 3650 lumens (Philips 138446 - PL-L 55W/950/4P - NAED 20725 - 55 Watt - 4 Pin 2G11 Base - 5300K - CFL Light Bulb). HTGsupply claims their bulbs put out 5000 lumens (High Tech Garden Supply). One poster said he bought Dulux-L bulbs which was specified at 4800 lumens, but the package said 3000 lumens (Wiring TG11 Socket Remote CFL lamps - International Cannagraphic Magazine Forums). Here is one by GE that lists it as 4100 lumens (http://www.1000bulbs.com/product/2327/FC55-BXCINEMA56.html)

How can the same type of 55w bulbs create different lumen outputs? If they really are 3000-3650 lumens, then they are in fact, much less efficient than 2 standard 2' T5-HO 24w tubes. Are there any experts here that can resolve this confusion? I really feel that these lumen claims are exaggerated or there are significant differences in how the lumens of the different bulbs were measured. The 2' 24w T5-HO consistently specify 2000 lumens across the board, while these lesser known PL-L's are highly variable in their specified lumen output.