Porch Boards (T&G) Filling the Gap

[historicalwork]

Hi All, i noticed another current / similar porched thread but decided i'd still start one here. I have a couple boards on our back porch entrance that need replacing (rotting at the end). I went to a salvage place and found some older boards with the right width, thickness and T&G. Of course, the boards there now are not all exactly the same width. Some are 3" some are 3 1/4", etc. I'm curious to know what was traditionally used to fill gaps between boards. In the picture i posted, you can see a typical example. There are areas where there is a filler of sorts. I see the same on our larger front porch. When i've done patching on windows, etc, i've used the two part abatron wood epox. Caulk doesn't seem like the right answer. What makes sense in these cases?

[1918ColonialRevival]

The picture isn't showing up for me, but I've seen strands of oakum used to fill small gaps between boards before. It was common to see it used in wooden ships in the 1920s and earlier (the days when the coastal schooners moved much of the freight).

[historicalwork]

Sorry about that - picture fixed.

[Catheetiem]

I have something kind of similar (as far as I can tell) in my 1870 house. I don't know when it was put in, but it's some sort of hard, clay-ish sort of material that's breaking apart and coming out of the cracks. Harder than the wood around it, it seems. I'll take a picture tonight and post it.

Everything I've been reading regarding wood filling makes it seem like flexibility is key, especially if it's going to be outside and undergoing significant temperature/humidity changes. It needs to be able to expand and contract with the wood.