if your holes are within an inch or so of the bottom, you are probably okay for the season if you are using a 5-1-1 mix, which drains quickly. if you are using straight MG you need better drainage. for a clearer understanding of drainage issues/needs, try reading the following thread ...

container soils 101: 5-1-1 and gritty mix

I personally like holes on the sides. The holes in the bottom can get blocked and can also let tree roots come up from the bottom and invade the pot. I live in the south and the little extra water in the bottom can give more water for the hot months.

I think your pots have drainage holes but they drain into the trays which I personally do not like. I had one and did like you, just drilled 4 or 5 one inch holes in the sides and I have not had any problems.

Where you live can make a difference as well as soil type. I would agree that if you're using straight MG or any similarly dense/peaty soil, your plants would probably be better off if you unpotted and added a goodly amount of perlite to the soil. (The 5-1-1 would be better still, but if that is not in the cards this season, don't sweat it.)

If you are reasonably confident as to the quality of the soil and are only concerned about drainage and wish to add more drainage holes, simply tilt the pots to gain access to their bottoms and drill away. The soil will not pose any measurable obstacle to the drill bit.

Agree. Holes in the sides near the bottom are fine. Soil quality is more important. Faster draining is better.

If you feel it's not draining adequately, you could try adding wicks to the holes, but I think you should be fine.