While I'm not completely certain of the method of remanufacturing, my thinking is that "recycled" lamps reuse the non-expendable portions of the lamp assembley (the metal hosuing, the wiring harness and the reflective outer glass shell), replacing only the filament envelope.
Please note, this is an anecdote - it by no means implies you will have the same results by using a "recycled" bulb. We noticed recycled bulbs tended to meet their demise prematurely, sometimes violently (shattering). Infrequently, this resulted in damage to the first prismatic lens directly facing the open lamp cavity. Upon examination our remanufactured lamps were found to fail at the adhesive bond where the new filament envelope was affixed to the original housing. Perhaps the thermal incompatability of two differently stressed pieces of glass led to this; I'm not certain. The temperatures involved in this area are certainly extremely high. I would estimate recycled bulb life to be approximately 2/3 to 3/4 that of a factory fresh genuine replacement (bulbs rated for 1000 hours) under ideal conditions; in our sample useage, recycled lamp brighness was nearly always somewhat diminished.
While QC has gotten much better in this respect in the past couple of years, and our experience was from three or so years ago, we found it more economical over the long run to simply buy genuine replacement bulb assemblies (particularly when dealing with 100 + LCD projectors). A full, healthy bulb lifespan is hopefully a bit more certain when purchasing original replacements (or a close facsimile thereof) - though no lightbulb can be guaranteed to last for its entire rated lifespan, despite their cost.
Of course, YMMV.