Stuy Town and Peter Cooper Village tenants suing property owner Tishman Speyer had another big day yesterday, when the state's highest court heard arguments in a trial that could set a costly precedent for landlords at rent-regulated buildings citywide. The tenants' lawyers said Tishman's conversion of rent-regulated apartments into market-rate units was illegal because the developer received tax abatement, something the state legislature forbids. But Tishman's lawyers argued that the law doesn't apply to them because the apartments became rent-stabilized 18 years before the developers got the tax breaks. A semantic debate about the word "become" ensued, with Judge Robert S. Smith finally asking, "You might say that I became a grandfather for the third time last month. Isn’t that normal English, even though I was already a grandfather?" (His point, seemingly, was that the law's use of the word "became" shouldn't be so strictly interpreted by Tishman.) But the bigger question yesterday hinged on what impact a verdict for the tenants would have—they're seeking some $200 million in damages from Tishman, whose lawyers warned that landlords could have to repay “tens, if not hundreds, of millions of dollars” to tenants who were overcharged, should the Appeals court uphold the lower court's ruling.