No idea on how Titleist specifically, adjusts weight on irons to hit a SW goal. Other OEMs use a variety of weights epoxied into the head or hosel, or added via screws, etc.

As to tipping, and I didn't understand this either at first, it's a way to make a stiffer by taking length away from the less stiff end of the shaft. Let's say for a wood, the plain raw shaft is 46" long. You want your driver to be 44.5" though, and the adapter will add about 1" of length, plus the head itself adds some length, call it 1/2". Clearly, you need to trim the shaft from 47.5 to 44.5 in order to get the length you want. You need to cut 3" off somewhere.

For a lot of shafts, the manufacturer will instruct you to trim from the butt end only, and start tipping only when fitting a fairway wood. "Tipping" means you're trimming off the tip end vs the butt end. Instead of losing 3" of butt, where the shaft is wider, and therefore stiffer, you tip 1", and butt trim only 2". That extra 1" of shaft butt makes the whole assembly stiffer. It's a way to fine-tune a fit, similar to hard- or soft-stepping.

For woods tipping is done to achieve the the correct flex for the specific wood # the shaft is being fitted i.e. Driver, 3 wood, 5 wood etc.. So tipping starts with the Driver and is adjusted (increased) for each subsequent wood.

For irons tipping only appllies to .370 tip shafts which are called parallel tiip shafts. These shafts are produced in one specific length (Manufacturer and Model dependent) and then tipped for each iron # to achieve the flex required for the specific iron #. As you go from the 2 iron to wedges the tipping increases so the final shaft weight changes from club to club, thus, the shafts are also called "decending weight" shafts.

The other iron shafts are .355 tapered tip shafts. Each tapered shaft has been manufactured to fit a specific iron # and are often referred to as "discrete length" shafts. Each iron in a set of tapered tip shafts is the same weight so these shafts are also called "constant weight" shafts". Ttileist only use .355 tapered iron shafts.

When custom ordering irons, it is important to specify D3/D4. Otherwise they will be built to D1-D2.

Cast/forged heads all vary by weight - just a fact. On receipt, Titleist separates the accepted heads into at least 2 bins - lighter and heavier. They may have an average bin as well. In your case, your order will be pulled from the heavier bin. Including the grips and adjusted shaft and length, the swing weight is tested. The system then instructs the assembler which (metal) weight to include in the hosel to get to the swing weight ordered. Then the sw is tested again to meet spec.

The iron shafts are trimmed to length at the butt end. Tipping refers more to how metalwoods are adjusted for feel. In the case of irons, the analogous practice is to hard/soft step the shafts. Using a 6 iron shaft or 8 iron shaft in a 7 iron will adjust the feel. Taking more off a 6 shaft from the butt will feel firmer, and less off of an 8 shaft will feel softer in the 7 iron.

I don’t play enough golf to say this will change my game by hard/soft stepping shafts.

Installing an 7 iron shaft in a 6 iron or hard stepping makes for a stiffer club while putting a 5 iron in that same 6 iron or soft stepping makes for a more flexible club. Taking more or less from the butt to produce a shorter than standard or longer than standard club length will not normally effect the feel and/or stiffness of the club. An overlength or under length club length has no relation to soft stepping or hard stepping.