I cannot post more than two links, so I have only linked to the most important things.
Most Stargates use a normal glyph as a Point of Origin – these are not unique. Some Stargates have a special Point of Origin – these are typically thought to be unique, but might act as the same missing glyph.
In a number of episodes, it can be seen that a normal glyph is used as the Point of Origin for a planet. Knowing Earth's address, the extra lit glyph on the DHDs in Shades of Grey, New Ground, and Memento must be the Point of Origin for the respective planet. You can see that Memento's Tagrea and New Ground's P2X-416 have the same Point of Origin glyph. Thus, there does not appear to be a problem with reusing Point of Origin glyphs, and logically cannot be given the number of Stargates in the Milky Way network.
However, this raises a different issue. If a planet's Point of Origin is a normal glyph, this would mean that any other planet that contains that glyph in their address would not be able to be dialed. This would imply that a single location would not be able to reach every Stargate in the galaxy, unless under special circumstances.
Related to this is the point that Milky Way Stargates have 39 glyphs on the inner track. However, Milky Way DHDs only have 38 glyphs. Thus, one glyph from the Stargate is always missing on the DHD. In the image of Abydos' DHD, the Aquila glyph is missing (most other planets' DHDs are missing this glyph as well). We often see that Earth's special glyph appears on the DHDs of planets that use a normal glyph as their Point of Origin, including in The Tok'ra, Part 1, Cure, Memento, and Demons. This could mean that the special glyph is completely unused on those planets, that it acts as the missing Aquila glyph only on those planets, or that it is not as special as first assumed and is in fact a normal glyph.
@Richard – Izkata beat me to it; Destiny's hardware address specifically requires the symbol used for Earth's Point of Origin. It is on the Icarus Base's DHD (kind of blurry, but you can just make it out).