Symfony 3.4 apply tag on all classes who implement same interface

I'm working with a Symfony 3.4 (PHP 7.2, update to 7.4 soon) project. I have some classes who extends an abstract class and i would like all my classes got the same constant name (constant have value different in each class). I'm starting with a pattern like this :

abstract class AbstractClass
{
    abstract public function getConstant(): string;
}

final class Foo extends AbstractClass
{
    const MY_CONST = 'foo';

    public function getConstant(): string
    {
        return self::MY_CONST;
    }
}

final class Bar extends AbstractClass
{
    const MY_CONST = 'bar';

    public function getConstant(): string
    {
        return self::MY_CONST;
    }
}

// echo $foo->getConstant() : 'foo'
// echo $bar->getConstant() : 'bar'

The goal: if a class who extends AbstractClass don't have MY_CONST, i want return an message error. I have excluded theses solutions :

• I can't add a constant in an interface (maybe in PHP 8 ?)
• I can't use "abstract factory" pattern for a constant (in my code it runs with getConstant() method
• I can't use a static property

The only way i have found is : implement an interface and tag the interface like explain in documentation. With compilerpass, helped with ReflexionClass, i will check if constant name exist, and if not: thrown an error or something like this.

So, i've edit like this :

final class Foo extends AbstractClass implements MyCustomInterface
{
     // ...
}

final class Bar extends AbstractClass implements MyCustomInterface
{
    // ...
}

The interface :

interface MyCustomInterface
{
}

Adding tag in AppKernel.php

    protected function build(ContainerBuilder $container): void
    {
        $container
            ->registerForAutoconfiguration(MyCustomInterface::class)
            ->addTag('my_custom_tag');
    }

And a compilerpass :

class MyCustomPass implements CompilerPassInterface
{
    public function process(ContainerBuilder $container): void
    {
        if (!$container->has(MyCustomInterface::class)) {
            dump('No interface found');
            return;
        }

        $definition = $container->findDefinition(MyCustomInterface::class);
        $taggedServices = $container->findTaggedServiceIds('my_custom_tag');
        dump($taggedServices);
    }
}

The fun begin here...if i have only ONE class who implement the interface, $taggedServices find the service. BUT, if more than one class implements interface, no class are found...

I don't find where i am wrong. Do i need to implements AbstractClass instead of children classes ?