There are no 75cl bottles of french '87 listed on winesearcher pro world wide. odds on, not findable.
2005 is a similar problem, as if declared, it has not yet been released. will not until 07 or 08.
20 year old champagne is an acquired taste, and if originally bottled in 91 or 92, will not be much of a thrill in my opinion. most 20 year old that is a big deal comes out on a re-release in the few years prior to consumption.
time in bottle can pretty much be determined by the behavior of the pulled cork.
5 years in the bottle, and the cork is rock hard, and does not expand.