Consider code like:
lib:
---
public abstract sealed class Lib permits Impl1, Impl2 {}
final class Impl1 extends Lib {}
final class Impl2 extends Lib {}
---
test:
---
public class Test1 {
    public void test(Lib lib) {
        Runnable r = (Runnable) lib;
    }
}
public class Test2 {
    public void test(Lib lib) {
        switch (lib) {
            case Impl2 i -> {}
        }
    }
}
---

If Impl1 is missing, the behavior differs:
---
$ javac -d out -classpath out --enable-preview -source 17 test/Test1.java
test/Test1.java:3: error: cannot access Impl1
        Runnable r = (Runnable) lib;
                     ^
  class file for Impl1 not found
1 error
---
$ javac -d out -classpath out --enable-preview -source 17 test/Test2.java
test/Test2.java:3: error: the switch statement does not cover all possible input values
        switch (lib) {
        ^
Note: test/Test2.java uses preview features of Java SE 17.
Note: Recompile with -Xlint:preview for details.
1 error
---

The switch handling should be more consistent with the case, and should report an error on missing classfiles for the permitted subtypes.