This is a very interesting thread and something I seem to spend much time looking into. I too noticed all the 1821 Guatemala 1/4 reales appearing over several weeks at Heritage, any details of the hoard? There appear to be some other dates/mints which have an unusually high number of mint state examples which would also suggest hoards, for example the 1811 4 and 8 reales struck in Valencia - I can't seem to find any details on a hoard for these - not surprisng though given the seige of the city by Napoleon's forces in 1812 - anyone?
As suggested there are usually high grade examples of most British and British colonial coinage available however for the other series I collect such a France, Spain and Italy of the Napoleonic period I have slowly (very slowly ) started to look into this in more detail. It has been surprising how little is recorded, how few mint state examples there are and also how 'rare' some of the issues appear to be particularly for the minor denominations.
For example part of my Journal Entry 'In Search of Varieities'
"Even though the 1808M issue has the second highest mintage of the short series at 87,183, and that it also has the most graded examples - 37 coins graded at NGC (VF to MS64) and 9 at PCGS (XF40 to AU58) it still does not appear very often. To complicate matters further there are 3 varieties of this coin - Type 1 which is extremely rare and Type 2 which is the version that is usually found. The Type 2 coins are further split into 2 varieties depending on the number of stars on each side of the standard on the reverse, one has 3 stars and the other 6, hopefully the attached scans highlight the difference between the two varieties. As I now have both of these varieties in my collection I decided to look into the possible populations and my research so far suggests that the existing population of Type 2 1808M 20 Lire coins is most likely less than 150 coins with VF being the typical grade encountered and that the 3 stars variety is about twice as prevelant as the 6 stars variety. Although both NGC and PCGS do not yet distinguish between these known varieties on the label what was surprising was that the vast majority of higher grade examples are already in TPG holders and that these also account for a significant portion of the existing examples! It should also be noted that, at the moment, I am only aware of a single mint state example, either raw or graded and that is the NGC MS64 '3 stars' example sold by Heritage in January 2015 for $3525, as this is way beyond my budget, and that it also has some light adjustment marks across the middle of the reverse, I am more than happy with my '2nd finest AU58' example."
Gold coinage seems to be more available and well documented compared to silver and copper issues, and in the several Journal entries (e.g. Collecting the Small Coins - Spanish Charles IV 2 reales) I have started to consider the smaller denominations of the period. As this study progresses it appears that some issues have very few recorded examples (<10) with no graded examples at all and that the finest documented may be VF. Although I expect, and hope, that quality coins are to be found in long-standing private collections (e.g. Journal Entry on the 1808I 10 centimes: If you wait long enough....) it does mean that some lower grade, problem free coins that I would have passed on at auction I now actively bid on as it may be the only chance to actually complete a set .