user12957: The FIDE rating regulations say:

8.5 Determining the rating change for a rated player
8.51 For each game played against a rated player, determine the difference in rating between the player and his opponent, D. [...]
8.54 A difference in rating of more than 400 points shall be counted for rating purposes as though it were a difference of 400 points.
8.55
(a) Use table 8.1(b) to determine the player’s score probability PD [...]

But table 8.1b (which seems to be used only for this purpose) contains entries that go higher than 400. What use are those entries? Why are they there in the first place if they cannot be used?

user12629: Table 8.1(a) is also used by reference in the title regulations. To achieve a GM, IM, WGM, or WIM norm, a player must have a performance rating over a certain amount, and the performance rating is calculated using this table. Unlike the rating regulations, the title regulations do not limit the ratings difference to 400 points, so the entire table is used.
Table 8.1(b) is pretty much the inverse of 8.1(a).

user4418: 
Why are they there in the first place if they cannot be used?

They were there in the first place because they were used. The 400 point rule came later.

What use are those entries?

They provide interesting historical context which makes it easier to answer questions like this.
Perhaps a better question would be, why are they still there, or why weren't they removed when the 400 point rule was introduced. There are two obvious answers:

Inertia. It would take effort to remove them
Efficiency. If the 400 point rule is rescinded at some stage then the entries required are already there. 


12957: <p>The <a href="https://old.fide.com/fide/handbook.html?id=197&amp;view=article" rel="noreferrer">FIDE rating regulations</a> say:</p>
<blockquote>
<p>8.5 Determining the rating change for a rated player</p>
<p>8.51 For each game played against a rated player, determine the difference in rating between the player and his opponent, D. [...]</p>
<p>8.54 A difference in rating of more than 400 points shall be counted for rating purposes as though it were a difference of 400 points.</p>
<p>8.55
(a) Use table 8.1(b) to determine the player’s score probability PD [...]</p>
</blockquote>
<p>But table 8.1b (which seems to be used only for this purpose) contains entries that go higher than 400. What use are those entries? Why are they there in the first place if they cannot be used?</p>
 12629: <p>Table 8.1(a) is also used by reference in the <a href="https://handbook.fide.com/chapter/B01Regulations2017" rel="nofollow noreferrer">title regulations</a>. To achieve a GM, IM, WGM, or WIM norm, a player must have a performance rating over a certain amount, and the performance rating is calculated using this table. Unlike the rating regulations, the title regulations do not limit the ratings difference to 400 points, so the entire table is used.</p>

<p>Table 8.1(b) is pretty much the inverse of 8.1(a).</p>
 4418: <blockquote>
  <p>Why are they there in the first place if they cannot be used?</p>
</blockquote>

<p>They were there in the first place because they <em>were</em> used. The 400 point rule came later.</p>

<blockquote>
  <p>What use are those entries?</p>
</blockquote>

<p>They provide interesting historical context which makes it easier to answer questions like <a href="https://chess.stackexchange.com/questions/29518/how-does-elo-rating-gain-scale-with-games-played">this</a>.</p>

<p>Perhaps a better question would be, why are they still there, or why weren't they removed when the 400 point rule was introduced. There are two obvious answers:</p>

<ol>
<li>Inertia. It would take effort to remove them</li>
<li>Efficiency. If the 400 point rule is rescinded at some stage then the entries required are already there. </li>
</ol>
