There's not really a question here, but I happen to have read that paper just now. I'll try to provide my interpretation.
- This sentence states that Scuttlebut reconciliation will not differ from precise reconciliation if there was no maximum to the size of network messages. Obviously, there is; this is the whole point of coming up with a clever reconciliation mechanism.
- This sentence states that there can be no gaps in the sequence of changes (deltas) that are part of a single Scuttlebut message. If a particular change is not transmitted in some message, then it is not allowed to include any change that is more recent that the omitted message. So in short: a message always contains a set of changes that are the oldest among changes not known to the peer that will receive the message.
- The invariant ensures that for each key k in the set of state variables, participant q either has the current value of k present at participant p, or the version number (or timestamp) of the current value at p is higher than the maximum version number of all values at p that q knows about. All in all, this has to do with the absence of gaps again.
Writing this up has made things more clearer for myself, hope it helps you :)
(feel free to comment when things are still too fuzzy)