Sure! Let's create a test case generator for the "Run Length Encoding" problem. The generator will create multiple compressed strings, each with a mix of plain characters and encoded sequences using the "@" notation.

Here's a possible implementation in Python:

```python
import random
import string

def generate_compressed_string():
    original = []
    length = random.randint(1, 100)  # Length of the original string is up to 100 characters
    i = 0
    
    while i < length:
        # Decide whether to add a normal character or a compressed sequence
        if random.choice([True, False]) and i + 2 <= length:  # Ensure there's space for a compressed sequence
            char = random.choice(string.ascii_letters + string.digits + string.punctuation)
            count = random.randint(2, 9)  # 2 to 9 consecutive characters
            original.append(f"@{count}{char}")
            i += 2  # One character for '@' and one for the count
        else:
            original.append(random.choice(string.ascii_letters + string.digits + string.punctuation))
            i += 1
    
    return ''.join(original)

def tcgen():
    num_strings = random.randint(1, 50)  # Number of strings, up to 50
    test_cases = [generate_compressed_string() for _ in range(num_strings)]
    return test_cases

if __name__ == "__main__":
    test_cases = tcgen()
    for tc in test_cases:
        print(tc)
```

### Explanation:

1. **generate_compressed_string()**:
    - This function generates a single compressed string.
    - It randomly decides whether to add a plain character or an encoded sequence.
    - Plain characters are chosen from uppercase and lowercase letters, digits, and symbols.
    - Encoded sequences use the "@" notation with a subsequent digit (2 to 9) and a character.

2. **tcgen()**:
    - This function generates a list of compressed strings, with the number of strings being up to 50.
    - Each string is generated using the `generate_compressed_string()` function.

To use this generator, simply call the `tcgen()` function, and it will return a list of compressed strings as test cases. Each string can be printed or used directly in testing environments.

This setup ensures that each test case adheres to the constraints given in the problem statement and provides a diverse set of inputs for robust testing.