If properly packed and if the cork is OK, there is no limit. The alcohol has no expiration date.
Bottles are suspended over the pear buds (upside down) before they get too big (the buds not the bottle), and the pear grows in the bottle. I have been very successful in doing that for the last ten years or so.
They place empty bottles directly on the fruit trees where the fruit bud is made to grow inside each bottle.
When the pear is growing they hang a bottle over the small growing pear. At this time the pear is small enough to put a bottle over it. As the pear ripens, its grows inside the bottle. When the pear is ready to be harvested they take the bottle with the pear "trapped" inside. Then it is off to the distillery where they fill the bottle.
The bottle is attached to a branch and the pear grows inside the bottle.
Many makers of pear brandy bottle it with a pear in the bottle. Ironworks Distillery in Nova Scotia is one. Most large liquor stores in the US that I have been in have had at least one variety of pear brandy that included a pear in the bottle.
While the pear is small it is placed in the bottle, and the bottle is supported in the tree. Pear reaches full size in the bottle.
Once the pear gets to a certain size they will place the bottle on the branch of the pear and allow it to grow to fit the bottle.
To make pear-in-the-bottle they actually grow the pear inside of the bottle in their orchards, and then fill it with their pear eau de vie. This practice of growing pears in the bottle is traditional in Alsace where pear brandy has been made for hundreds of years. Pear-in-the-bottle is highly labor intensive, requiring weeks of work putting the bottles on the trees in late May when the small pear will still fit in the neck of the bottle, tending them all summer, and picking them in late August. Since they use no preservatives or artificial cleaning solutions, each pear and each bottle must be painstakingly scrubbed by hand before they fill it with their pear eau de vie for which they are known worldwide. Due to the unpredictable nature of pear growth from year to year the pear in the bottle is only available certain years.
The pear grew in the bottle.
Unopened liquor will expire eventually. It will last much longer unopened than it will when it is opened and exposed to air.
Not sure if this is the case here, but it would be possible to place the bottle's opening over the pear when it is still very young, on the branch and small enough to fit in the opening. They could allow it to mature that way, harvest and rinse when ripe, then fill and seal the bottle. Again, I'm not sure this is the way it is officially done. I'm just saying that it is one possibility.
A bottle is attached to the end of a pear tree branch and the pear grows inside the bottle.