Measured OG higher than estimated

I'm new here, and fairly new to brewing, but been lurking awhile. Learned lots on this site.

I've had a couple brews that have come out with actual OGs higher than estimated in BeerSmith (and double-checked in other software, such as ProMash trial version).

The first was an English Pale Ale, where the actual OG was about 8 pts higher than estimated, and the second was a stout where the actual OG was 12 pts higher. I'm wondering if I'm doing something wrong in entering the ingredients, or other info such as volume, into the software... the details for the stout:

6 lb amber DME (Beermeister, San Leandro, CA)
12.5 oz Corn Syrup Extract Crystal (leftover Mr. Beer Booster - entered into software as corn sugar)
1 lb Crystal Malt 60L
0.5 lb black patent malt
0.5 lb roasted barley
2 oz Northern Brewer hops (60 min)
0.75 oz Willamette hops (10 min)
1.75 tsp gypsum
Wyeast 1084 liquid yeast - Irish Ale

5 gallon batch. The estimated OG was 1.071 in BeerSmith, the actual OG was 1.083.

I can't remember what the OGs were for the English Pale Ale (my brew log is at home and I'm at work), but the ingredients didn't include the Mr. Beer booster or the amber DME, which I was thinking were the most likely culprits in causing the difference in measured vs. estimated OG in the software... It was a simple recipe, with only liquid UME (I think maybe 6 lbs) and 1 lb Crystal Malt 60L. I've checked my hydrometer, it reads 1.000 @ 60F. I also made a porter recently with amber DME, entered the info into the software the same as I had with the pale ale and stout (same volumes etc), and my actual OG came out exactly as estimated...

Any ideas why the actual OG was higher than estimated for the pale ale and stout? Efficiency even at 100% doesn't explain it, nor does the batch volume (to "correct" the estimated OG for what I actually got, I have to bring the volume down to 4.2 gal - there's no way I was that far off with the volume into the fermenter - it was definitely very close to 5 gal. The fermentation was so vigorous with the stout that I lost about 1/2 gallon through the blow-off tube within 2-3 days).

On the upside, at least the OGs have been higher than expected rather than lower!

I would think that your efficiency is set low in beersmith because you are getting a higher efficiency your OG would be off, in your case it would come out on the high side.

So I would suggest increasing your efficiency % in beersmith to match your OG then the next time you brew calculate your efficiency and enter them numbers for a more accurate %.

Thanks. I thought of that, but to correct the stout, efficiency would have been over 100%... There just weren't enough grains to make that much of a difference.

One more thing, since my brew kettle isn't large enough to boil an entire 5 gal batch, I add about 3 gal of wort to water in the carboy, then shake the carboy. Maybe I didn't shake it enough, both times - I definitely thought I did, mostly to get oxygen in there.