This is an old post but I'll try to summarize it:

In Wordnet 3.0
00119533 00 s 01 lifeless 0 003 & 00119409 a 0000 + 14006179 n 0103 + 05006285 n 0102

In Wordnet 2.1
00138191 00 s 02 dead 0 lifeless 0 003 & 00138067 a 0000 + 13820045 n 0203 + 04947580 n 0202

For the gloss:
lacking animation or excitement or activity; "the party being dead we left early"; "it was a lifeless party until she arrived"

For instance: typing lifeless in Wordnet 3.0:
1. (2) lifeless, exanimate -- (deprived of life; no longer living; "a lifeless body")

2. (1) lifeless -- (destitute or having been emptied of life or living beings; "after the dance the littered and lifeless ballroom echoed hollowly")

3.lifeless -- (lacking animation or excitement or activity; "the party being dead we left early"; "it was a lifeless party until she arrived")

4. lifeless -- (not having the capacity to support life; "a lifeless planet")

but in Wordnet 2.1:
1. (2) lifeless, exanimate -- (deprived of life; no longer living; "a lifeless body")

2. (1) lifeless -- (destitute or having been emptied of life or living beings; "after the dance the littered and lifeless ballroom echoed hollowly")

3. dead, lifeless -- (lacking animation or excitement or activity; "the party being dead we left early"; "it was a lifeless party until she arrived")

4. lifeless -- (not having the capacity to support life; "a lifeless planet").

There are pros and cons to each database and one is not necessarily better than the other.

The Cons:

A simple answer:

As demonstrated, in a contemporary setting, one could still describe a party as dead the same way it could be described as lifeless in the same sense.

A more technical answer:

Wordnet 3.0 left some examples in the glosses ("the party being dead we left early") but it did cut out the sense (dead) for some synset rows even after the new morph.c in the dict folder used the exc files. There are approximately 1000+ synset rows affected by this issue.

The Pros:

A simple answer:

If you look in the dict folder the file size is bigger for the exc file hinting that more words are added for irregular words (for instance: verb.exc) on the list is bigger.

A more technical answer:

Wordnet 3.0 has consolidated the data and index files and to make up for it, it added more senses so the index and data files are more interlinked with the sense file increasing the KB size. In addion, all the exc. files have a larger KB size meaning that there are more irregular words.

You can read the whole technical documentation given by others in this post for more info.