Where Are All The 1972 5c Coins?

I doubt they are deliberatly taking them out of circulation, I beliee it is the dillution from the massive issues of the 2000's, and natural loss through attrition.

Here are the key figures from my spreadsheet.
Up until 2008 the total number of 5c coins produced was
3972.8 million
1972 5c 8.4 million
Percentage of 5c coins which were 1972 is 0.2%
This would be 4 coins per $100 - but only IF there were NO coins removed from circulation eg lost/damaged/collected.
If 3% of coins are removed from circulation each year, then there would effectively only be 2.7 million 1972's still in circulation.
To adjust the "4 per $100" figure to take into account 3% loss each year
2.7 / 8.4 * 4 = 1.29
1.29 per $100 seems to also be very close to what I seem to be finding.
Is the 3% figure for coins being removed from circulation too high or low?
Is there anything I might have gotten wrong?
What do you all think?

Thanks for the feedback in2fish2.
I was beginning to think the stats were not of interest to anyone.
Your mention of the foreign coins reminded me of Enlil's comment about dillution. I have not taken into account that foreign coins have been added to the pool. From my noodling I think that there are usually between 10 and 20 foreign coins in $100 worth of 5c. That is between 0.5% and 1% of 5c so will have some dillution effect.
I also realised that I only worked out the 3% loss each year up until 2008, but since 3% was just a guess it probably does not matter too much.

You've done a fair bit of research ozcoins. Seems pretty accurate to me when looking at an average. These things still seem to annoy the heck out of me. I went through $210 last week and found none and then yesterday went through $50 and found 4. I know it seems stupid and is probably just luck of the draw but I swear I have better luck from some banks than others.