La Pavoni has manufactured the lever group Europiccola and Professional models for a long time now, and many changes and upgrades have occurred.
There are currently three versions of the Europiccola in existence. The first, original version, was produced in 1961. These had a single switch and no pan or grate under the group to collect extra water or coffee drips. This model also had a brass piston with the screen locked in place requiring a special tool or "key" to remove it. In 1970 the fixed screen version was revised into the removable version existing today. These older models also lacked a sight glass water level assembly. The sight glass assembly was added in 1972. The base was modified into a bowl shape that allowed it to accept a small cup grate in 1974. More, bigger changes took place in 1974: first, the group was redesigned to be held onto the boiler with two bolts, where previously it was threaded onto the boiler. Second, 1974 witnessed the introduction of the Professional model, so all of the changes that took place from 1961 until 1974 with the Europiccola were integrated directly in to the production line for the Professional. The Professional model was also produced with added electrical safety features that the Europiccola did not have, and would not have for some years. Both models were revised in 1980 to use a three bolt flange type of heating element where previously the elements threaded onto the boiler. Finally 1990 the Europiccola was revised to use a thermostat and pressurestat combination.
In the year 2000 both the Europiccola and Professional models were upgraded to a larger size group which is now referred to as the "MILLENNIUM EDITION".
The only to differences between the models is that the Professional has a larger volume boiler, and comes with a pressure gauge. The Europiccola is smaller and has no gauge (which is not an option to add/retro-fit). In order to tell which edition La Pavoni you have, and you do not know and cannot find the manufacture date, you will need to remove the lower base and look inside for a sticker that says "Millennium". If no sticker exists, it is a "pre-Millennium" edition, meaning it was manufactured before August of the year 2000. Unfortunately, this is not fail-safe way to tell, of course, as the sticker could have been lost or they neglected to put one on.
Another way to check is to measure your baskets. The Millennium editions have a larger portafilter basket. These accept a 51mm diameter tamper base. The older version portafilter baskets accept a 49mm tamper base so they are very close in size. You can also check the measurements of your portafilter, in the event you've lost the basket and cannot measure it. The Millennium edition portafilter bodies measure 54mm on the inside diameter. The older version portafilter bodies measure 52mm on the inside diameter. The MP (for Millennium Pavoni) 68 and MP69 baskets are for the Millennium edition, and the P68 and P69 baskets are for the older versions.
You can confirm your edition another way. The older versions do not have a black plastic insert behind the group head. By removing the group head, you can inspect it for this insert. You will want to have an o-ring (P45) on hand first to reseal the group in case the o-ring tears or won't re-seal.