The reason we might pass 1=4=3=5 hands was explained in the previous post. Hands with 4=1=3=5 shape are very similar: in particular, the singleton heart gives us a way to get back into the auction later if opponents bid hearts. The 4=1=3=5 shape is not quite so good for passing as 1=4=3=5, but the problems with finding an opening bid are the same. (In a standard "natural" system, on the other hand, it would be ridiculous to pass 4=1=3=5 hands with opening strength: there is no problem with either the opening bid or the rebid.)
Now, if a pass can be made on up to 13 HCP, we need to make some changes to the methods we use as a passed hand. In particular, there is a problem if partner opens 1-of-a-suit in third or fourth seat. Here we have the values for game unless partner has made a tactical light opening, but using traditional methods it is difficult to see how we can bid the hand. A natural 2C would normally be played as non-forcing by a passed hand, and in some circumstances a 2C response might even be played as artificial (Drury).
Since the "strong" hand types have such specific shapes, I think the solution is to use a specific response to show these hands. For example, over a 1S opening we could use a jump to 2NT to show the 1=4=3=5 type with 11-13 HCP. Normally most jumps by a passed hand are used to show hands with support for partner, but these do not come up particularly often, and with both opponents passing there is no particular need to have lots of bids which show support. So it makes a lot of sense to use some of the jumps for a new purpose.
If it is the opponents who open the bidding, there is not so much need for specifically-designed methods. If they bid one of our long suits there is no need to come into the bidding at all. If they bid our short suit, on the other hand, it is quite safe to come into the bidding even at relatively high levels, since a take-out double describes the hand very well. A take-out double does not necessarily show the "opening pass" type of hand - it could just be a normal maximum pass with ideal shape - but partner will be aware of the possibility.
The systemic pass on minimum 1=4=3=5 and 4=1=3=5 shapes makes a big difference to the 2C opening bid. The traditional Precision 2C opening shows either 6 clubs or 5 clubs and a 4-card major. Playing a systemic opening pass we can guarantee that if the hand does have only 5 clubs, it will be at the maximum end of the range. This is because, for weaker hands:
- With 1=4=3=5 or 4=1=3=5 we can pass;
- With 2=4=2=5 or 4=2=2=5 we can pretend the hand is balanced;
- With a hand short in diamonds we have an alternative opening bid available: a three-suited opening bid in traditional Precision, or a 1C opening in Polish Club.
When responding to a 2C opening this information is very helpful: it means we can investigate game with an invitational hand knowing that if opener does not have the values for game, he will always have a six-card club suit for us to fall back on. Whereas in standard Precision we might play an uncomfortable 2NT contract after 2C : 2D , 2M : 2NT, if minimum 5-4 hands are passed this sequence should probably be played as forcing, which in turn makes life easier for responder when he holds a strong hand.
Playing this agreement means that a 2C opening bid will only very rarely have precisely 5 clubs. Ideally we would like 2C to absolutely guarantee a 6-card suit. Some versions of Precision do this by putting the other hands into 1D, but a systemic pass is a very good alternative for the minimum hands. A more extreme version of the systemic opening pass would pass all hands in range for 2C if the shape was right, but now you get to the point where partner will want to allow for the strong type when deciding whether to open the bidding; once this happens you are not really playing a standard system any more. Of course, there is not necessarily anything wrong with unusual systems, and it would be amusing to see how a genuine two-way pass system would fare, for example:
Pass = 0-10 HCP any shape, or 11-16 HCP unbalanced with 4+ clubs and a 4-card major
1C = 11-13 HCP balanced / 44(41), or any hand with 17+ HCP
1D = 5+ diamonds, 11-16 HCP
1H = 5+ hearts, 11-16 HCP
1S = 5+ spades, 11-16 HCP
1NT = 14-16 HCP balanced / 44(41)
2C = 5+ clubs, no 4-card major, 11-16 HCP
Partner would be expected to open in 3rd or 4th seat with any 9+ HCP. Perhaps this sort of thing should not be taken too seriously, but it might be worryingly playable. (Except that it's almost certainly illegal, of course.)