yisrael yid – true selling or doing an issur with shviis wine does not change the status; if it was in the hands of an reliable hechsher at time of biur then we are meikel that it is considered hefker since the otzar beis din are not owners only as shluchim of the zibur; and we rely on the ramban and rash that peiros that werw hefker at time of biur doas not become asur. it should be noted that according to most sfardim it is asur even if it was hefker as is the opinion of the rambam and many rishonim.
the main problem is that an otzar beis din is not hokus pokus; the whole heter of otzar beis din is not clear cut; there is no clear mkor for the otzar beis din that we have now days; although it is based on a tosefta according to the explanation of some rishonim; others explain the tosefta differently also the rambam does not mention otzar beis din- evan those that were matir theotzar beis din as the chazon ish [and rabbanim; of eideh chareidis for esrogim only] was on condition that it is not sold regularly in stores prices have to be cheaper.
for the above reasons there are hardly wines sold by otzar beis din; and some [even those that have good hechsharim the otheryears do heter mechirah in shmitah] since these wines are being sold by the componey regular in the stores according to all major poskim in eretz yisroal can not be considered that it was in hands of otzar beis din.
regarding destroying wine after biur- I don’t know what you heard from your rabaaim but the halacha is very clear – before zman biur there is an isur of ‘hefsed peiros shviis’ but anything that is chayev biur could be mvuer the way it is; just like chametz erev pesach is not baal tashcis and just like trumah that has to be burnt as trumah has the exact same kdusha as shviis as is clear in the Mishnah. you could open up mishnaus and all rishonim as well as rambam and nosei keilim in hilchos biur; and it is clear that at time of biur everything has to be destroyed without mention of spoiling.
I am absolutely sure of the psak from elyashiv and I remember all the detailes it was a few shmitos ago [1994] and the chidush was that he said to spill the wine just because the biur wasn’t done properly [it was done by shliach]
